Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 17,577	$ 7,490
Available for sale, gross unrealized losses less than 12 months	212	19
Available for sale, fair value 12 months or longer	1,257	1,351
Available for sale, gross unrealized losses 12 months or longer	4	7
Available for sale, fair value total	18,834	8,841
Available for sale, gross unrealized losses total	216	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	5,438	1,636
Available for sale, gross unrealized losses less than 12 months	39	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	5,438	1,636
Available for sale, gross unrealized losses total	39	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	3,753	1,394
Available for sale, gross unrealized losses less than 12 months	82	7
Available for sale, fair value 12 months or longer	11	63
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	3,764	1,457
Available for sale, gross unrealized losses total	82	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	9,191	3,030
Available for sale, gross unrealized losses less than 12 months	121	8
Available for sale, fair value 12 months or longer	11	63
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	9,202	3,093
Available for sale, gross unrealized losses total	121	8
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	985	1,498
Available for sale, gross unrealized losses less than 12 months	0	4
Available for sale, fair value 12 months or longer	234	369
Available for sale, gross unrealized losses 12 months or longer	1	2
Available for sale, fair value total	1,219	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	985	1,529
Available for sale, gross unrealized losses less than 12 months	0	4
Available for sale, fair value 12 months or longer	234	566
Available for sale, gross unrealized losses 12 months or longer	1	3
Available for sale, fair value total	1,219	2,095
Available for sale, gross unrealized losses total	1	7
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		600
Available for sale, gross unrealized losses less than 12 months		1
Available for sale, fair value 12 months or longer		120
Available for sale, gross unrealized losses 12 months or longer		1
Available for sale, fair value total		720
Available for sale, gross unrealized losses total		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	231	1,015
Available for sale, gross unrealized losses less than 12 months	0	3
Available for sale, fair value 12 months or longer	895	446
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	1,126	1,461
Available for sale, gross unrealized losses total	1	4
Non-U.S. debt securities, government securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,570	489
Available for sale, gross unrealized losses less than 12 months	1	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	1,570	489
Available for sale, gross unrealized losses total	1	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	4,618	715
Available for sale, gross unrealized losses less than 12 months	81	3
Available for sale, fair value 12 months or longer	71	80
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	4,689	795
Available for sale, gross unrealized losses total	81	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	6,419	2,819
Available for sale, gross unrealized losses less than 12 months	82	7
Available for sale, fair value 12 months or longer	966	646
Available for sale, gross unrealized losses 12 months or longer	1	2
Available for sale, fair value total	7,385	3,465
Available for sale, gross unrealized losses total	83	9
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	60	95
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	46	76
Available for sale, gross unrealized losses 12 months or longer	2	2
Available for sale, fair value total	106	171
Available for sale, gross unrealized losses total	2	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	922	17
Available for sale, gross unrealized losses less than 12 months	9	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	922	17
Available for sale, gross unrealized losses total	$ 9	$ 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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