Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 26,519	$ 7,490
Available for sale, gross unrealized losses less than 12 months	171	19
Available for sale, fair value 12 months or longer	872	1,351
Available for sale, gross unrealized losses 12 months or longer	7	7
Available for sale, fair value total	27,391	8,841
Available for sale, gross unrealized losses total	178	26
US Treasury and federal agencies, direct obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	11,538	1,636
Available for sale, gross unrealized losses less than 12 months	63	1
Available for sale, fair value 12 months or longer	0	0
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	11,538	1,636
Available for sale, gross unrealized losses total	63	1
US Treasury and federal agencies, mortgage-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	3,847	1,394
Available for sale, gross unrealized losses less than 12 months	41	7
Available for sale, fair value 12 months or longer	162	63
Available for sale, gross unrealized losses 12 months or longer	2	0
Available for sale, fair value total	4,009	1,457
Available for sale, gross unrealized losses total	43	7
Total U.S. Treasury and federal agencies
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	15,385	3,030
Available for sale, gross unrealized losses less than 12 months	104	8
Available for sale, fair value 12 months or longer	162	63
Available for sale, gross unrealized losses 12 months or longer	2	0
Available for sale, fair value total	15,547	3,093
Available for sale, gross unrealized losses total	106	8
Non-U.S. debt securities, mortgage-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	394	600
Available for sale, gross unrealized losses less than 12 months	1	1
Available for sale, fair value 12 months or longer	33	120
Available for sale, gross unrealized losses 12 months or longer	0	1
Available for sale, fair value total	427	720
Available for sale, gross unrealized losses total	1	2
Non-U.S. debt securities, asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	646	1,015
Available for sale, gross unrealized losses less than 12 months	1	3
Available for sale, fair value 12 months or longer	464	446
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	1,110	1,461
Available for sale, gross unrealized losses total	2	4
Non-U.S. sovereign, supranational and non-U.S. agency
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	5,631	489
Available for sale, gross unrealized losses less than 12 months	42	0
Available for sale, fair value 12 months or longer	39	0
Available for sale, gross unrealized losses 12 months or longer	1	0
Available for sale, fair value total	5,670	489
Available for sale, gross unrealized losses total	43	0
Non-U.S. debt securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,291	715
Available for sale, gross unrealized losses less than 12 months	17	3
Available for sale, fair value 12 months or longer	67	80
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	1,358	795
Available for sale, gross unrealized losses total	17	3
Total non-U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	7,962	2,819
Available for sale, gross unrealized losses less than 12 months	61	7
Available for sale, fair value 12 months or longer	603	646
Available for sale, gross unrealized losses 12 months or longer	2	2
Available for sale, fair value total	8,565	3,465
Available for sale, gross unrealized losses total	63	9
Asset-backed securities, student loans
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months		31
Available for sale, gross unrealized losses less than 12 months		0
Available for sale, fair value 12 months or longer		197
Available for sale, gross unrealized losses 12 months or longer		1
Available for sale, fair value total		228
Available for sale, gross unrealized losses total		1
Asset-backed securities, collateralized loan obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,516	1,498
Available for sale, gross unrealized losses less than 12 months	1	4
Available for sale, fair value 12 months or longer	62	369
Available for sale, gross unrealized losses 12 months or longer	0	2
Available for sale, fair value total	2,578	1,867
Available for sale, gross unrealized losses total	1	6
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,516	1,529
Available for sale, gross unrealized losses less than 12 months	1	4
Available for sale, fair value 12 months or longer	62	566
Available for sale, gross unrealized losses 12 months or longer	0	3
Available for sale, fair value total	2,578	2,095
Available for sale, gross unrealized losses total	1	7
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	83	95
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	45	76
Available for sale, gross unrealized losses 12 months or longer	3	2
Available for sale, fair value total	128	171
Available for sale, gross unrealized losses total	3	2
Other U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	573	17
Available for sale, gross unrealized losses less than 12 months	5	0
Available for sale, fair value 12 months or longer	0	0
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	573	17
Available for sale, gross unrealized losses total	$ 5	$ 0

Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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