Fair value measurements - Schedule of quantitative and qualitative information regarding significant unobservable inputs (Detail) - Recurring [Member] - Level 3 [Member] ¥ in Billions		6 Months Ended		12 Months Ended
		Sep. 30, 2022 JPY (¥)		Mar. 31, 2022 JPY (¥)		Jun. 30, 2022 JPY (¥)	Sep. 30, 2021 JPY (¥)	Jun. 30, 2021 JPY (¥)	Mar. 31, 2021 JPY (¥)
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 928		¥ 792		¥ 909	¥ 663	¥ 624	¥ 566
Fair Value, Financial Instrument, Liabilities		493		580		534	629	639	694
Trading assets and private equity and debt investments [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		478		398		469	364	397	366
Trading assets and private equity and debt investments [Member] | Equities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 16		¥ 14		19	12	11	16
Trading assets and private equity and debt investments [Member] | Equities [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	Not applicable		Not applicable
Trading assets and private equity and debt investments [Member] | Equities [Member] | DCF [Member] | Liquidity discounts [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.75		0.75
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Equities [Member] | DCF [Member] | Liquidity discounts [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.75		0.75
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 39		¥ 32		32	47	45	58
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | WACC [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | WACC [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.053		0.071
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | WACC [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.175		0.13
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | WACC [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.098		0.102
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Growth rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Growth rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0		0
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Growth rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.02		0.02
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Growth rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.005		0.007
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Credit spreads [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.109
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.109
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Liquidity discounts [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Liquidity discounts [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.05		0.05
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Liquidity discounts [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.30		0.30
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Liquidity discounts [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.181		0.185
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | EV/EBITDA ratios [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | EV/EBITDA ratios [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	(0.4)		2
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | EV/EBITDA ratios [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	11.6		11.2
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | EV/EBITDA ratios [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	7.1		6.9
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | PE Ratios [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | PE Ratios [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	10.9		10.7
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | PE Ratios [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	24		12.6
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | PE Ratios [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	14.2		11.6
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | Liquidity discounts [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | Liquidity discounts [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.05		0.05
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | Liquidity discounts [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.30		0.20
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | Liquidity discounts [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.129		0.119
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 10		¥ 10		12	10	13	12
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Credit spreads [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0		0
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.013		0.013
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.007		0.007
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Recovery rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]			0.06
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Recovery rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.073
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Recovery rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.185
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Recovery rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.082		0.06
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 272		¥ 220		260	132	131	135
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Credit spreads [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0		0.001
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	1.547		1.147
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.087		0.072
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Recovery rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Recovery rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0		0
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Recovery rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	1		1
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Recovery rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.821		0.844
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 7		¥ 7		7	8	8	8
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Yields [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Yields [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.046		0.043
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Yields [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.127		0.111
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Yields [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.049		0.046
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Loss severities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Loss severities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.283		0.283
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Loss severities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.73		0.73
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.403		0.408
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 9		¥ 8		9	7	7	6
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Yields [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Yields [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0		0
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Yields [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.25		0.222
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Yields [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.088		0.084
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Prepayment rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Prepayment rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.072		0.069
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Prepayment rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.15		0.15
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Prepayment rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.097		0.095
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Loss severities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Loss severities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.003		0
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Loss severities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.999		0.999
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.173		0.069
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 103		¥ 79		105	123	158	106
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	Not applicable		Not applicable
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member] | Loss severities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member] | Loss severities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.014		0
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member] | Loss severities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.202		0.212
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.077		0.029
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 20		¥ 26		23	23	21	23
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	Change in default probabilities typically accompanied by directionally similar change in loss severities and opposite change in prepayment rates		Change in default probabilities typically accompanied by directionally similar change in loss severities and opposite change in prepayment rates
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Yields [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Yields [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.068		0.055
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Yields [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.30		0.275
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Yields [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.192		0.131
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Prepayment rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.20
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Prepayment rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]			0.18
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Prepayment rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]			0.20
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Prepayment rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.20		0.195
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Default probabilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.02		0.02
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Default probabilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.02		0.02
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Loss severities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Loss severities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	0.955		0
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Loss severities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[2]	1		1
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading assets and private equity and debt investments	[5],[6]	0.968		0.44
Equity contracts [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets	[7]	¥ (5)		¥ 10		26	9	(39)	(41)
Equity contracts [Member] | Option models [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Equity contracts [Member] | Option models [Member] | Dividend yield [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Equity contracts [Member] | Option models [Member] | Dividend yield [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0		0
Equity contracts [Member] | Option models [Member] | Dividend yield [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.315		0.126
Equity contracts [Member] | Option models [Member] | Dividend yield [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Equity contracts [Member] | Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Equity contracts [Member] | Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.055		0
Equity contracts [Member] | Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	1.112		1.097
Equity contracts [Member] | Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Equity contracts [Member] | Option models [Member] | Correlations [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Equity contracts [Member] | Option models [Member] | Correlations [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	(0.8)		(0.8)
Equity contracts [Member] | Option models [Member] | Correlations [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.97		0.97
Equity contracts [Member] | Option models [Member] | Correlations [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Interest rate contracts [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets	[7]	¥ 35		¥ (11)		20	(28)	(41)	(43)
Interest rate contracts [Member] | DCF / Option models [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Interest rate contracts [Member] | DCF / Option models [Member] | Interest rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Interest rate contracts [Member] | DCF / Option models [Member] | Interest rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.012		0.003
Interest rate contracts [Member] | DCF / Option models [Member] | Interest rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.045		0.033
Interest rate contracts [Member] | DCF / Option models [Member] | Interest rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.103		0.092
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.171		0.139
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.00388		0.00348
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.01472		0.01283
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Interest rate contracts [Member] | DCF / Option models [Member] | Correlations [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Interest rate contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	(1)		(1)
Interest rate contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.99		0.98
Interest rate contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Credit contracts [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets	[7]	¥ (33)		¥ (33)		(30)	(37)	(31)	(38)
Credit contracts [Member] | DCF / Option models [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Credit contracts [Member] | DCF / Option models [Member] | Credit spreads [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Credit contracts [Member] | DCF / Option models [Member] | Credit spreads [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.001		0
Credit contracts [Member] | DCF / Option models [Member] | Credit spreads [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	4.474		4.287
Credit contracts [Member] | DCF / Option models [Member] | Credit spreads [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Credit contracts [Member] | DCF / Option models [Member] | Recovery rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Credit contracts [Member] | DCF / Option models [Member] | Recovery rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0		0
Credit contracts [Member] | DCF / Option models [Member] | Recovery rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.90		0.90
Credit contracts [Member] | DCF / Option models [Member] | Recovery rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Credit contracts [Member] | DCF / Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Credit contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.595		0.50
Credit contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.685		0.676
Credit contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Credit contracts [Member] | DCF / Option models [Member] | Correlations [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Credit contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.24		0
Credit contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.9		0.9
Credit contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Foreign exchange contracts [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets	[7]	¥ 21		¥ 10		18	10	9	15
Foreign exchange contracts [Member] | Option models [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Foreign exchange contracts [Member] | Option models [Member] | Interest rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Foreign exchange contracts [Member] | Option models [Member] | Interest rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.036		0.003
Foreign exchange contracts [Member] | Option models [Member] | Interest rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.036		0.029
Foreign exchange contracts [Member] | Option models [Member] | Interest rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.024		0.024
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.431		0.393
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0		0.00139
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0		0.0024
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Foreign exchange contracts [Member] | Option models [Member] | Correlations [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Foreign exchange contracts [Member] | Option models [Member] | Correlations [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	(1)		(0.25)
Foreign exchange contracts [Member] | Option models [Member] | Correlations [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[2]	0.84		0.84
Foreign exchange contracts [Member] | Option models [Member] | Correlations [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Derivatives, net	[5],[6]
Loans and receivables [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 221		¥ 205		196	123	111	104
Loans and receivables [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Loans and receivables [Member] | DCF [Member] | Credit spreads [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Loans and receivables [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Loans and receivables	[2]	0		0
Loans and receivables [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Loans and receivables	[2]	0.674		0.215
Loans and receivables [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Loans and receivables	[5],[6]	0.078		0.06
Loans and receivables [Member] | DCF [Member] | Recovery rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Loans and receivables [Member] | DCF [Member] | Recovery rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Loans and receivables	[2]	0.40		0.44
Loans and receivables [Member] | DCF [Member] | Recovery rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Loans and receivables	[2]	1		1
Loans and receivables [Member] | DCF [Member] | Recovery rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Loans and receivables	[5],[6]	0.951		0.982
Collateralized agreements [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 19		¥ 16		18	13	16	18
Collateralized agreements [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	Not applicable		Not applicable
Collateralized agreements [Member] | DCF [Member] | Repo rate [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Collateralized agreements [Member] | DCF [Member] | Repo rate [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Collateralized agreements	[2]	0.028		0.028
Collateralized agreements [Member] | DCF [Member] | Repo rate [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Collateralized agreements	[2]	0.06		0.06
Collateralized agreements [Member] | DCF [Member] | Repo rate [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Collateralized agreements	[5],[6]	0.034		0.036
Non-trading debt securities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 3				3
Non-trading debt securities [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship
Non-trading debt securities [Member] | DCF [Member] | Credit spreads [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2]	0
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value
Non-trading debt securities [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[5],[6]	0
Other [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Assets		¥ 189	[8]	¥ 197	[8]	189	209	202	185
Other [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1],[8]	No predictable interrelationship		No predictable interrelationship
Other [Member] | DCF [Member] | WACC [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	0.118		0.101
Impact of increases in significant unobservable valuation inputs	[3],[4],[8]	Lower fair value		Lower fair value
Other [Member] | DCF [Member] | WACC [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[5],[6],[8]	0.118		0.101
Other [Member] | DCF [Member] | Growth rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	0.03		0.02
Impact of increases in significant unobservable valuation inputs	[3],[4],[8]	Higher fair value		Higher fair value
Other [Member] | DCF [Member] | Growth rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[5],[6],[8]	0.03		0.02
Other [Member] | DCF [Member] | Liquidity discounts [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	0.10		0.10
Impact of increases in significant unobservable valuation inputs	[3],[4],[8]	Lower fair value		Lower fair value
Other [Member] | DCF [Member] | Liquidity discounts [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[5],[6],[8]	0.10		0.10
Other [Member] | Market multiples [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1],[8]	Generally changes in multiples result in a corresponding similar directional change in a fair value measurement, assuming earnings levels remain constant.		Generally changes in multiples result in a corresponding similar directional change in a fair value measurement, assuming earnings levels remain constant.
Other [Member] | Market multiples [Member] | EV/EBITDA ratios [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4],[8]	Higher fair value		Higher fair value
Other [Member] | Market multiples [Member] | EV/EBITDA ratios [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	3.8		3.6
Other [Member] | Market multiples [Member] | EV/EBITDA ratios [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	5.3		5.9
Other [Member] | Market multiples [Member] | EV/EBITDA ratios [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[5],[6],[8]	4.3		4.4
Other [Member] | Market multiples [Member] | PE Ratios [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4],[8]	Higher fair value		Higher fair value
Other [Member] | Market multiples [Member] | PE Ratios [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	8.2		6.7
Other [Member] | Market multiples [Member] | PE Ratios [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	30.8		30.8
Other [Member] | Market multiples [Member] | PE Ratios [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[5],[6],[8]	10.8		13.1
Other [Member] | Market multiples [Member] | Price/Book ratios [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4],[8]	Higher fair value		Higher fair value
Other [Member] | Market multiples [Member] | Price/Book ratios [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	0.3		0.3
Other [Member] | Market multiples [Member] | Price/Book ratios [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	1.6		1.7
Other [Member] | Market multiples [Member] | Price/Book ratios [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[5],[6],[8]	0.8		0.9
Other [Member] | Market multiples [Member] | Liquidity discounts [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4],[8]	Lower fair value		Lower fair value
Other [Member] | Market multiples [Member] | Liquidity discounts [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	0.25		0.25
Other [Member] | Market multiples [Member] | Liquidity discounts [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[2],[8]	0.30		0.40
Other [Member] | Market multiples [Member] | Liquidity discounts [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other assets	[5],[6],[8]	0.299		0.306
Trading liabilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Liabilities		¥ 5		¥ 3		6	6	2	7
Trading liabilities [Member] | Equities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Liabilities		1		0		1	0	0	0
Trading liabilities [Member] | Foreign government, agency and municipal securities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Liabilities		0		0		0	0	0	1
Trading liabilities [Member] | Collateralized debt obligations ("CDOs") and other [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Liabilities				0		0	0	0	1
Trading liabilities [Member] | Bank and corporate debt securities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Liabilities		¥ 4		¥ 3		5	6	2	5
Trading liabilities [Member] | Bank and corporate debt securities [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	Not applicable		Not applicable
Trading liabilities [Member] | Bank and corporate debt securities [Member] | DCF [Member] | Recovery rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Trading liabilities [Member] | Bank and corporate debt securities [Member] | DCF [Member] | Recovery rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading liabilities	[2]	0.056		0.039
Trading liabilities [Member] | Bank and corporate debt securities [Member] | DCF [Member] | Recovery rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading liabilities	[2]	0.985		0.97
Trading liabilities [Member] | Bank and corporate debt securities [Member] | DCF [Member] | Recovery rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Trading liabilities	[5],[6]	0.858		0.841
Short-term borrowings [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Liabilities		¥ 29		¥ 58		35	86	94	103
Short-term borrowings [Member] | DCF / Option models [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Short-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Short-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Short-term borrowings	[2]	0.115		0.05
Short-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Short-term borrowings	[2]	1.112		0.97
Short-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Short-term borrowings	[5],[6]
Short-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Short-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Short-term borrowings	[2]	(0.65)		(0.8)
Short-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Short-term borrowings	[2]	0.97		0.93
Short-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Short-term borrowings	[5],[6]
Payables and deposits [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Liabilities		¥ 21		¥ 8		25	2	2	1
Payables and deposits [Member] | DCF / Option models [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Payables and deposits [Member] | DCF / Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Payables and deposits [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Payables and deposits	[2]	0.103		0.092
Payables and deposits [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Payables and deposits	[2]	0.113		0.113
Payables and deposits [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Payables and deposits	[5],[6]
Payables and deposits [Member] | DCF / Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]			Higher fair value
Payables and deposits [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Payables and deposits	[2]			0.00412
Payables and deposits [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Payables and deposits	[2]			0.00696
Payables and deposits [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Payables and deposits	[5],[6]
Payables and deposits [Member] | DCF / Option models [Member] | Correlations [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Payables and deposits [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Payables and deposits	[2]	0.34		0.34
Payables and deposits [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Payables and deposits	[2]	0.98		0.98
Payables and deposits [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Payables and deposits	[5],[6]
Long-term borrowings [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Liabilities		¥ 415		¥ 479		442	511	508	547
Long-term borrowings [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	Not applicable		Not applicable
Long-term borrowings [Member] | DCF [Member] | Loss severities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[2]	0		0
Impact of increases in significant unobservable valuation inputs	[3],[4]	Lower fair value		Lower fair value
Long-term borrowings [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[5],[6]	0		0
Long-term borrowings [Member] | DCF / Option models [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	No predictable interrelationship		No predictable interrelationship
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[2]	0.103		0.05
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[2]	1.112		0.97
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[5],[6]
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[2]	0.00669
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[2]			0.00412
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[2]			0.00696
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[5],[6]
Long-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member]
Quantitative information about significant unobservable inputs [Line Items]
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Long-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[2]	(1)		(1)
Long-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[2]	0.98		0.98
Long-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Long-term borrowings	[5],[6]
Other liabilities [Member]
Quantitative information about significant unobservable inputs [Line Items]
Fair Value, Financial Instrument, Liabilities		¥ 23		¥ 32		¥ 26	¥ 24	¥ 33	¥ 35
Other liabilities [Member] | DCF [Member]
Quantitative information about significant unobservable inputs [Line Items]
Interrelationships between valuation inputs	[1]	Not applicable		Not applicable
Other liabilities [Member] | DCF [Member] | Recovery rates [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other liabilities	[2]			0.90
Impact of increases in significant unobservable valuation inputs	[3],[4]	Higher fair value		Higher fair value
Other liabilities [Member] | DCF [Member] | Recovery rates [Member] | Minimum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other liabilities	[2]	0.908
Other liabilities [Member] | DCF [Member] | Recovery rates [Member] | Maximum [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other liabilities	[2]	0.985
Other liabilities [Member] | DCF [Member] | Recovery rates [Member] | Weighted Average [Member]
Quantitative information about significant unobservable inputs [Line Items]
Valuation inputs, Other liabilities	[5],[6]	0.927		0.90

[1] Consideration of the interrelationships between significant unobservable valuation inputs is only relevant where more than one unobservable valuation input is used to determine the fair value measurement of the financial instrument.

[2] Range information is provided in percentages, coefficients and multiples and represents the highest and lowest level significant unobservable valuation input used to value that type of financial instrument. A wide dispersion in the range does not necessarily reflect increased uncertainty or subjectivity in the valuation input and is typically just a consequence of the different characteristics of the financial instruments themselves.

[3] The above table only considers the impact of an increase in each significant unobservable valuation input on the fair value measurement of the financial instrument. However, a decrease in the significant unobservable valuation input would have the opposite effect on the fair value measurement of the financial instrument. For example, if an increase in a significant unobservable valuation input would result in a lower fair value measurement, a decrease in the significant unobservable valuation input would result in a higher fair value measurement.

[4] The impact of an increase in the significant unobservable valuation input on the fair value measurement for a derivative assumes Nomura is long risk to the input e.g., long volatility. Where Nomura is short such risk, the impact of an increase would have a converse effect on the fair value measurement of the derivative.

[5] Nomura has not provided weighted average information for derivatives as unlike cash products the risk on such products is distinct from the balance sheet value and is subject to netting.

[6] Weighted average information for non-derivatives is calculated by weighting each valuation input by the fair value of the financial instrument.

[7] Derivatives which contain multiple types of risk are classified based on the primary risk type of the instrument.

[8] Valuation techniques and unobservable valuation inputs in respect of equity securities reported within Other assets in the consolidated balance sheets.