Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 8,491	$ 12,428
Available for sale, gross unrealized losses less than 12 months	74	50
Available for sale, fair value 12 months or longer	1,558	2,626
Available for sale, gross unrealized losses 12 months or longer	12	24
Available for sale, fair value total	10,049	15,054
Available for sale, gross unrealized losses total	86	74
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	350	1,430
Available for sale, gross unrealized losses less than 12 months	0	28
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	350	1,430
Available for sale, gross unrealized losses total	0	28
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	1,001	2,499
Available for sale, gross unrealized losses less than 12 months	5	7
Available for sale, fair value 12 months or longer	124	1,665
Available for sale, gross unrealized losses 12 months or longer	1	18
Available for sale, fair value total	1,125	4,164
Available for sale, gross unrealized losses total	6	25
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	1,351	3,929
Available for sale, gross unrealized losses less than 12 months	5	35
Available for sale, fair value 12 months or longer	124	1,665
Available for sale, gross unrealized losses 12 months or longer	1	18
Available for sale, fair value total	1,475	5,594
Available for sale, gross unrealized losses total	6	53
Asset-backed securities, student loans
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	268	271
Available for sale, gross unrealized losses less than 12 months	7	1
Available for sale, fair value 12 months or longer	71	127
Available for sale, gross unrealized losses 12 months or longer	0	1
Available for sale, fair value total	339	398
Available for sale, gross unrealized losses total	7	2
Asset-backed securities, credit cards
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	0	89
Available for sale, gross unrealized losses less than 12 months	0	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	0	89
Available for sale, gross unrealized losses total	0	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	1,586	862
Available for sale, gross unrealized losses less than 12 months	25	2
Available for sale, fair value 12 months or longer	283	278
Available for sale, gross unrealized losses 12 months or longer	5	1
Available for sale, fair value total	1,869	1,140
Available for sale, gross unrealized losses total	30	3
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,854	1,222
Available for sale, gross unrealized losses less than 12 months	32	4
Available for sale, fair value 12 months or longer	354	405
Available for sale, gross unrealized losses 12 months or longer	5	2
Available for sale, fair value total	2,208	1,627
Available for sale, gross unrealized losses total	37	6
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	1,246	228
Available for sale, gross unrealized losses less than 12 months	6	0
Available for sale, fair value 12 months or longer	206	220
Available for sale, gross unrealized losses 12 months or longer	2	1
Available for sale, fair value total	1,452	448
Available for sale, gross unrealized losses total	8	1
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	1,483	672
Available for sale, gross unrealized losses less than 12 months	13	1
Available for sale, fair value 12 months or longer	105	109
Available for sale, gross unrealized losses 12 months or longer	2	1
Available for sale, fair value total	1,588	781
Available for sale, gross unrealized losses total	15	2
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	1,145	3,246
Available for sale, gross unrealized losses less than 12 months	7	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	1,145	3,246
Available for sale, gross unrealized losses total	7	1
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	856	2,736
Available for sale, gross unrealized losses less than 12 months	7	9
Available for sale, fair value 12 months or longer	747	187
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	1,603	2,923
Available for sale, gross unrealized losses total	8	10
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	4,730	6,882
Available for sale, gross unrealized losses less than 12 months	33	11
Available for sale, fair value 12 months or longer	1,058	516
Available for sale, gross unrealized losses 12 months or longer	5	3
Available for sale, fair value total	5,788	7,398
Available for sale, gross unrealized losses total	38	14
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	344	163
Available for sale, gross unrealized losses less than 12 months	3	0
Available for sale, fair value 12 months or longer	22	22
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	366	185
Available for sale, gross unrealized losses total	4	1
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months		13
Available for sale, gross unrealized losses less than 12 months		0
Available for sale, fair value 12 months or longer		4
Available for sale, gross unrealized losses 12 months or longer		0
Available for sale, fair value total		17
Available for sale, gross unrealized losses total		0
Other U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	212	219
Available for sale, gross unrealized losses less than 12 months	1	0
Available for sale, fair value 12 months or longer	0	14
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	212	233
Available for sale, gross unrealized losses total	$ 1	$ 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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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 unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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