Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 9,605	$ 12,428
Available for sale, gross unrealized losses less than 12 months	38	50
Available for sale, fair value 12 months or longer	1,243	2,626
Available for sale, gross unrealized losses 12 months or longer	8	24
Available for sale, fair value total	10,848	15,054
Available for sale, gross unrealized losses total	46	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		1,430
Available for sale, gross unrealized losses less than 12 months		28
Available for sale, fair value 12 months or longer		0
Available for sale, gross unrealized losses 12 months or longer		0
Available for sale, fair value total		1,430
Available for sale, gross unrealized losses total		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	3,295	2,499
Available for sale, gross unrealized losses less than 12 months	6	7
Available for sale, fair value 12 months or longer	98	1,665
Available for sale, gross unrealized losses 12 months or longer	1	18
Available for sale, fair value total	3,393	4,164
Available for sale, gross unrealized losses total	7	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	3,295	3,929
Available for sale, gross unrealized losses less than 12 months	6	35
Available for sale, fair value 12 months or longer	98	1,665
Available for sale, gross unrealized losses 12 months or longer	1	18
Available for sale, fair value total	3,393	5,594
Available for sale, gross unrealized losses total	7	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	215	271
Available for sale, gross unrealized losses less than 12 months	2	1
Available for sale, fair value 12 months or longer	47	127
Available for sale, gross unrealized losses 12 months or longer	0	1
Available for sale, fair value total	262	398
Available for sale, gross unrealized losses total	2	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		89
Available for sale, gross unrealized losses less than 12 months		1
Available for sale, fair value 12 months or longer		0
Available for sale, gross unrealized losses 12 months or longer		0
Available for sale, fair value total		89
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	1,471	862
Available for sale, gross unrealized losses less than 12 months	12	2
Available for sale, fair value 12 months or longer	339	278
Available for sale, gross unrealized losses 12 months or longer	4	1
Available for sale, fair value total	1,810	1,140
Available for sale, gross unrealized losses total	16	3
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,686	1,222
Available for sale, gross unrealized losses less than 12 months	14	4
Available for sale, fair value 12 months or longer	386	405
Available for sale, gross unrealized losses 12 months or longer	4	2
Available for sale, fair value total	2,072	1,627
Available for sale, gross unrealized losses total	18	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	900	228
Available for sale, gross unrealized losses less than 12 months	3	0
Available for sale, fair value 12 months or longer	280	220
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	1,180	448
Available for sale, gross unrealized losses total	4	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	1,389	672
Available for sale, gross unrealized losses less than 12 months	6	1
Available for sale, fair value 12 months or longer	111	109
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	1,500	781
Available for sale, gross unrealized losses total	7	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	279	3,246
Available for sale, gross unrealized losses less than 12 months	1	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	279	3,246
Available for sale, gross unrealized losses total	1	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	1,255	2,736
Available for sale, gross unrealized losses less than 12 months	5	9
Available for sale, fair value 12 months or longer	291	187
Available for sale, gross unrealized losses 12 months or longer	0	1
Available for sale, fair value total	1,546	2,923
Available for sale, gross unrealized losses total	5	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	3,823	6,882
Available for sale, gross unrealized losses less than 12 months	15	11
Available for sale, fair value 12 months or longer	682	516
Available for sale, gross unrealized losses 12 months or longer	2	3
Available for sale, fair value total	4,505	7,398
Available for sale, gross unrealized losses total	17	14
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	140	163
Available for sale, gross unrealized losses less than 12 months	1	0
Available for sale, fair value 12 months or longer	77	22
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	217	185
Available for sale, gross unrealized losses total	2	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	661	219
Available for sale, gross unrealized losses less than 12 months	2	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	661	233
Available for sale, gross unrealized losses total	$ 2	$ 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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