Loans and Allowance for Credit Losses - Amortized Cost Basis (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	$ 6,609	$ 3,935
Financing receivable, originated, year two	897	2,313
Financing receivable, originated, year three	2,141	1,918
Financing receivable, originated, year four	1,733	1,272
Financing receivable, originated, year five	1,162	495
Financing receivable, originated more than five years before current fiscal year	326	95
Revolving Loans	17,836	17,897
Loans, gross	30,704	27,925
Interest income	73	72
Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	25,155	22,583
Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	5,331	5,224
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	110	67
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	92	34
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	16	17
Geographic Distribution, Domestic
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	22,000	21,132
Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	8,704	6,793
Commercial and Financial Segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	28,370	25,829
Commercial and Financial Segment | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	23,243	20,859
Commercial and Financial Segment | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	4,909	4,852
Commercial and Financial Segment | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	110	67
Commercial and Financial Segment | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	92	34
Commercial and Financial Segment | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	16	17
Commercial and Financial Segment | Geographic Distribution, Domestic
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	3,078	2,326
Financing receivable, originated, year two	522	1,363
Financing receivable, originated, year three	1,245	826
Financing receivable, originated, year four	739	816
Financing receivable, originated, year five	700	272
Financing receivable, originated more than five years before current fiscal year	69	0
Revolving Loans	13,313	13,433
Loans, gross	19,666	19,036
Commercial and Financial Segment | Geographic Distribution, Domestic | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	2,309	1,894
Financing receivable, originated, year two	15	388
Financing receivable, originated, year three	409	4
Financing receivable, originated, year four	4	167
Financing receivable, originated, year five	157	200
Financing receivable, originated more than five years before current fiscal year	0	0
Revolving Loans	12,937	12,836
Loans, gross	15,831	15,489
Commercial and Financial Segment | Geographic Distribution, Domestic | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	769	432
Financing receivable, originated, year two	507	942
Financing receivable, originated, year three	745	822
Financing receivable, originated, year four	681	610
Financing receivable, originated, year five	509	43
Financing receivable, originated more than five years before current fiscal year	69	0
Revolving Loans	376	597
Loans, gross	3,656	3,446
Commercial and Financial Segment | Geographic Distribution, Domestic | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	0	0
Financing receivable, originated, year two	0	28
Financing receivable, originated, year three	48	0
Financing receivable, originated, year four	28	39
Financing receivable, originated, year five	34	0
Financing receivable, originated more than five years before current fiscal year	0	0
Revolving Loans	0	0
Loans, gross	110	67
Commercial and Financial Segment | Geographic Distribution, Domestic | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	0	0
Financing receivable, originated, year two	0	5
Financing receivable, originated, year three	43	0
Financing receivable, originated, year four	26	0
Financing receivable, originated, year five	0	29
Financing receivable, originated more than five years before current fiscal year	0	0
Revolving Loans	0	0
Loans, gross	69	34
Commercial and Financial Segment | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	3,173	1,311
Financing receivable, originated, year two	197	401
Financing receivable, originated, year three	347	346
Financing receivable, originated, year four	248	179
Financing receivable, originated, year five	185	26
Financing receivable, originated more than five years before current fiscal year	31	66
Revolving Loans	4,523	4,464
Loans, gross	8,704	6,793
Commercial and Financial Segment | Non-U.S. | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	2,929	1,028
Financing receivable, originated, year two	0	0
Financing receivable, originated, year three	0	0
Financing receivable, originated, year four	0	0
Financing receivable, originated, year five	0	0
Financing receivable, originated more than five years before current fiscal year	0	0
Revolving Loans	4,483	4,343
Loans, gross	7,412	5,371
Commercial and Financial Segment | Non-U.S. | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	244	283
Financing receivable, originated, year two	197	401
Financing receivable, originated, year three	347	346
Financing receivable, originated, year four	225	162
Financing receivable, originated, year five	169	26
Financing receivable, originated more than five years before current fiscal year	31	66
Revolving Loans	40	121
Loans, gross	1,253	1,405
Commercial and Financial Segment | Non-U.S. | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	0
Financing receivable, originated, year two	0
Financing receivable, originated, year three	0
Financing receivable, originated, year four	23
Financing receivable, originated, year five	0
Financing receivable, originated more than five years before current fiscal year	0
Revolving Loans	0
Loans, gross	23
Commercial and Financial Segment | Non-U.S. | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	0	0
Financing receivable, originated, year two	0	0
Financing receivable, originated, year three	0	0
Financing receivable, originated, year four	0	17
Financing receivable, originated, year five	16	0
Financing receivable, originated more than five years before current fiscal year	0	0
Revolving Loans	0	0
Loans, gross	16	17
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,334	2,096
Commercial real estate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,912	1,724
Commercial real estate | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	422	372
Commercial real estate | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Commercial real estate | Geographic Distribution, Domestic
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	358	298
Financing receivable, originated, year two	178	549
Financing receivable, originated, year three	549	746
Financing receivable, originated, year four	746	277
Financing receivable, originated, year five	277	197
Financing receivable, originated more than five years before current fiscal year	226	29
Revolving Loans	0	0
Loans, gross	2,334	2,096
Commercial real estate | Geographic Distribution, Domestic | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	238	178
Financing receivable, originated, year two	129	383
Financing receivable, originated, year three	383	688
Financing receivable, originated, year four	688	277
Financing receivable, originated, year five	277	197
Financing receivable, originated more than five years before current fiscal year	197	0
Revolving Loans	0	0
Loans, gross	1,912	1,723
Commercial real estate | Geographic Distribution, Domestic | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	120	120
Financing receivable, originated, year two	49	166
Financing receivable, originated, year three	166	58
Financing receivable, originated, year four	58	0
Financing receivable, originated, year five	0	0
Financing receivable, originated more than five years before current fiscal year	29	29
Revolving Loans	0	0
Loans, gross	$ 422	$ 373