Loans and Allowance for Credit Losses - Amortized Cost Basis (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	$ 8,199	$ 3,935
Financing receivable, originated, year two	867	2,313
Financing receivable, originated, year three	2,079	1,918
Financing receivable, originated, year four	1,598	1,272
Financing receivable, originated, year five	1,055	495
Financing receivable, originated more than five years before current fiscal year	323	95
Revolving Loans	18,676	17,897
Loans, gross	32,797	27,925
Interest income	82	72
Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	26,899	22,583
Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	5,563	5,224
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	156	67
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	164	34
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	15	17
Geographic Distribution, Domestic
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	22,650	21,132
Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	10,147	6,793
Commercial and Financial Segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	30,413	25,829
Commercial and Financial Segment | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	24,936	20,859
Commercial and Financial Segment | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	5,180	4,852
Commercial and Financial Segment | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	118	67
Commercial and Financial Segment | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	164	34
Commercial and Financial Segment | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	15	17
Commercial and Financial Segment | Geographic Distribution, Domestic
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	3,670	2,326
Financing receivable, originated, year two	492	1,363
Financing receivable, originated, year three	1,236	826
Financing receivable, originated, year four	606	816
Financing receivable, originated, year five	618	272
Financing receivable, originated more than five years before current fiscal year	67	0
Revolving Loans	13,577	13,433
Loans, gross	20,266	19,036
Commercial and Financial Segment | Geographic Distribution, Domestic | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	2,696	1,894
Financing receivable, originated, year two	14	388
Financing receivable, originated, year three	376	4
Financing receivable, originated, year four	2	167
Financing receivable, originated, year five	135	200
Financing receivable, originated more than five years before current fiscal year	0	0
Revolving Loans	13,120	12,836
Loans, gross	16,343	15,489
Commercial and Financial Segment | Geographic Distribution, Domestic | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	974	432
Financing receivable, originated, year two	473	942
Financing receivable, originated, year three	719	822
Financing receivable, originated, year four	519	610
Financing receivable, originated, year five	455	43
Financing receivable, originated more than five years before current fiscal year	67	0
Revolving Loans	457	597
Loans, gross	3,664	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	70	0
Financing receivable, originated, year four	29	39
Financing receivable, originated, year five	19	0
Financing receivable, originated more than five years before current fiscal year	0	0
Revolving Loans	0	0
Loans, gross	118	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	5	5
Financing receivable, originated, year three	71	0
Financing receivable, originated, year four	56	0
Financing receivable, originated, year five	9	29
Financing receivable, originated more than five years before current fiscal year	0	0
Revolving Loans	0	0
Loans, gross	141	34
Commercial and Financial Segment | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	4,088	1,311
Financing receivable, originated, year two	197	401
Financing receivable, originated, year three	294	346
Financing receivable, originated, year four	277	179
Financing receivable, originated, year five	161	26
Financing receivable, originated more than five years before current fiscal year	31	66
Revolving Loans	5,099	4,464
Loans, gross	10,147	6,793
Commercial and Financial Segment | Non-U.S. | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	3,655	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	4,938	4,343
Loans, gross	8,593	5,371
Commercial and Financial Segment | Non-U.S. | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	433	283
Financing receivable, originated, year two	197	401
Financing receivable, originated, year three	294	346
Financing receivable, originated, year four	254	162
Financing receivable, originated, year five	146	26
Financing receivable, originated more than five years before current fiscal year	31	66
Revolving Loans	161	121
Loans, gross	1,516	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	15	0
Financing receivable, originated more than five years before current fiscal year	0	0
Revolving Loans	0	0
Loans, gross	15	17
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,384	2,096
Commercial real estate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,963	1,724
Commercial real estate | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	383	372
Commercial real estate | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	38	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	441	298
Financing receivable, originated, year two	178	549
Financing receivable, originated, year three	549	746
Financing receivable, originated, year four	715	277
Financing receivable, originated, year five	276	197
Financing receivable, originated more than five years before current fiscal year	225	29
Revolving Loans	0	0
Loans, gross	2,384	2,096
Commercial real estate | Geographic Distribution, Domestic | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated, year one	321	178
Financing receivable, originated, year two	129	383
Financing receivable, originated, year three	383	688
Financing receivable, originated, year four	657	277
Financing receivable, originated, year five	276	197
Financing receivable, originated more than five years before current fiscal year	197	0
Revolving Loans	0	0
Loans, gross	1,963	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	20	0
Financing receivable, originated, year five	0	0
Financing receivable, originated more than five years before current fiscal year	28	29
Revolving Loans	0	0
Loans, gross	383	$ 373
Commercial real estate | Geographic Distribution, Domestic | Special mention
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	38
Financing receivable, originated, year five	0
Financing receivable, originated more than five years before current fiscal year	0
Revolving Loans	0
Loans, gross	$ 38