Employee benefit plans (Tables)

12 Months Ended

Mar. 31, 2020

Employee Benefit Plans [Abstract]

Net periodic benefit cost for defined benefit plans

	Millions of yen
	Year ended March 31
	2018			2019			2020
Service cost	¥	9,565		¥	11,270		¥	12,079
Interest cost		2,258			2,180			1,766
Expected return on plan assets		(6,066	)		(6,068	)		(6,038	)
Amortization of net actuarial losses		2,979			3,831			5,654
Amortization of prior service cost		(1,061	)		(1,059	)		(1,137	)
Net periodic benefit cost	¥	7,675		¥	10,154		¥	12,324

Reconciliation of changes in projected benefit obligation and fair value of plan assets

	Millions of yen
	As of or for the year ended March 31
	2019			2020
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	¥	287,983		¥	315,423
Service cost		11,270			12,079
Interest cost		2,180			1,766
Actuarial gain		25,855			(5,642	)
Benefits paid		(11,953	)		(13,301	)
Amendments of pension benefit plans		—			(6,818	)
Acquisition, divestitures and other		88			16
Projected benefit obligation at end of year	¥	315,423		¥	303,523
Change in plan assets:
Fair value of plan assets at beginning of year	¥	234,050		¥	232,885
Actual return on plan assets		3,574			(2,934	)
Employer contributions		4,484			5,584
Benefits paid		(9,223	)		(9,791	)
Fair value of plan assets at end of year	¥	232,885		¥	225,744
Funded status at end of year		(82,538	)		(77,779	)
Amounts recognized in the consolidated balance sheets	¥	(82,538	)	¥	(77,779	)

Projected benefit obligation, accumulated benefit obligation and fair value of plan assets for pension plans with ABO and PBO in excess of plan assets

	Millions of yen
	March 31
	2019		2020
Plans with ABO in excess of plan assets:
PBO	¥	82,538	¥	77,779
ABO		82,538		77,779
Fair value of plan assets		—		—
Plans with PBO in excess of plan assets:
PBO	¥	82,538	¥	77,779
ABO		82,538		77,779
Fair value of plan assets		—		—

Amounts in accumulated other comprehensive income, pre-tax, that have not yet been recognized as components of net periodic benefit cost

	Millions of yen
	For the year ended March 31, 2020
Net actuarial loss	¥	107,098
Net prior service cost		(11,281	)
Total	¥	95,817

Amounts in accumulated other comprehensive income, pre-tax, expected to be recognized as components of net periodic benefit cost over next fiscal year

	Millions of yen
	For the year ending March 31, 2021
Net actuarial loss	¥	5,486
Net prior service cost		(1,601	)
Total	¥	3,885

Schedule of weighted-average assumptions used to determine PBO

	March 31
	2019			2020
Discount rate		0.6	%		0.6	%
Rate of increase in compensation levels		1.6	%		0.3	%

Weighted-average assumptions used to determine net periodic benefit costs

	Year ended March 31
	2018			2019			2020
Discount rate		0.9	%		0.8	%		0.6	%
Rate of increase in compensation levels		2.5	%		1.7	%		1.6	%
Expected long-term rate of return on plan assets		2.6	%		2.6	%		2.6	%

Information about plan assets at fair value

	Millions of yen
	March 31, 2019
	Level 1		Level 2		Level 3		Balance as of March 31, 2019
Pension plan assets:
Equities	¥	21,991	¥	—	¥	—	¥	21,991
Private equity and pooled investments(1)		—		9,145		3,823		12,968
Japanese government securities		25,980		—		—		25,980
Foreign government, agency and municipal securities		—		22		—		22
Bank and corporate debt securities		2,566		2,082		—		4,648
Investment trust funds and other(2)(3)		—		6,070		50,560		56,630
Life insurance company general accounts		—		64,437		—		64,437
Other assets		—		39,748		—		39,748
Total	¥	50,537	¥	121,504	¥	54,383	¥	226,424
	Millions of yen
	March 31, 2020
	Level 1		Level 2		Level 3		Balance as of March 31, 2020
Pension plan assets:
Equities	¥	—	¥	—	¥	—	¥	—
Private equity and pooled investments(1)		—		1,901		23,465		25,366
Japanese government securities		23,464		—		—		23,464
Foreign government, agency and municipal securities		—		—		—		—
Bank and corporate debt securities		—		—		—		—
Investment trust funds and other(2)(3)		—		22,027		41,616		63,643
Life insurance company general accounts		—		66,363		—		66,363
Other assets		—		40,508		—		40,508
Total	¥	23,464	¥	130,799	¥	65,081	¥	219,344

(1) Includes corporate type equity investments.

(2) Includes mainly debt investment funds. Hedge funds and real estate funds are also included.

(3) Certain assets that are measured at fair value using net asset value per share as a practical expedient have not been classified in the fair value hierarchy. As of March 31, 2019 and March 31, 2020, the fair values of these assets were ¥6,462 million and ¥6,401 million, respectively.

Information about plan assets for which Level 3 inputs are utilized to determine fair value

	Millions of yen
	Year ended March 31, 2019
	Balance as of April 1, 2018		Unrealized and realized gains / loss			Purchases / sales and other settlement			Balance as of March 31, 2019
Private equity and pooled investments	¥	3,639	¥	(349	)	¥	533		¥	3,823
Investment trust funds and other		48,088		937			1,535			50,560
Total	¥	51,727	¥	588		¥	2,068		¥	54,383
	Millions of yen
	Year ended March 31, 2020
	Balance as of April 1, 2019		Unrealized and realized gains / loss			Purchases / sales and other settlement			Balance as of March 31, 2020
Private equity and pooled investments	¥	3,823	¥	(4,403	)	¥	24,045		¥	23,465
Investment trust funds and other		50,560		(3,262	)		(5,682	)		41,616
Total	¥	54,383	¥	(7,665	)	¥	18,363		¥	65,081

Expected benefit payments

Year ending March 31	Millions of yen
2021	¥	13,167
2022		12,231
2023		12,733
2024		13,276
2025		14,049
2026-2030		63,956