Loans and Allowance for Credit Losses - Amortized Cost Basis (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
2021	$ 8,034	$ 3,935
2020	850	2,313
2019	2,200	1,918
2018	1,806	1,272
2017	1,222	495
Prior	560	95
Revolving Loans	16,913	17,897
Loans, gross	31,585	27,925
Interest income	105	72
Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	25,822	22,583
Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	5,509	5,224
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	111	67
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	127	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	22,723	21,132
Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	8,862	6,793
Commercial and Financial Segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	29,489	25,829
Commercial and Financial Segment | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	24,147	20,859
Commercial and Financial Segment | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	5,088	4,852
Commercial and Financial Segment | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	111	67
Commercial and Financial Segment | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	127	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]
2021	4,909	2,326
2020	496	1,363
2019	1,303	826
2018	780	816
2017	752	272
Prior	271	0
Revolving Loans	12,116	13,433
Loans, gross	20,627	19,036
Commercial and Financial Segment | Geographic Distribution, Domestic | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2021	4,563	1,894
2020	58	388
2019	385	4
2018	4	167
2017	162	200
Prior	200	0
Revolving Loans	11,767	12,836
Loans, gross	17,139	15,489
Commercial and Financial Segment | Geographic Distribution, Domestic | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
2021	346	432
2020	438	942
2019	822	822
2018	721	610
2017	556	43
Prior	42	0
Revolving Loans	349	597
Loans, gross	3,274	3,446
Commercial and Financial Segment | Geographic Distribution, Domestic | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	28
2019	48	0
2018	29	39
2017	34	0
Prior	0	0
Revolving Loans	0	0
Loans, gross	111	67
Commercial and Financial Segment | Geographic Distribution, Domestic | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	5
2019	48	0
2018	26	0
2017	0	29
Prior	29	0
Revolving Loans	0	0
Loans, gross	103	34
Commercial and Financial Segment | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2021	3,005	1,311
2020	176	401
2019	348	346
2018	280	179
2017	193	26
Prior	63	66
Revolving Loans	4,797	4,464
Loans, gross	8,862	6,793
Commercial and Financial Segment | Non-U.S. | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2,275	1,028
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior	0	0
Revolving Loans	4,733	4,343
Loans, gross	7,008	5,371
Commercial and Financial Segment | Non-U.S. | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
2021	730	283
2020	176	401
2019	348	346
2018	256	162
2017	177	26
Prior	63	66
Revolving Loans	64	121
Loans, gross	1,814	1,405
Commercial and Financial Segment | Non-U.S. | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	24
2017	0
Prior	0
Revolving Loans	0
Loans, gross	24
Commercial and Financial Segment | Non-U.S. | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	17
2017	16	0
Prior	0	0
Revolving Loans	0	0
Loans, gross	16	17
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,096	2,096
Commercial real estate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,675	1,724
Commercial real estate | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	421	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]
2021	120	298
2020	178	549
2019	549	746
2018	746	277
2017	277	197
Prior	226	29
Revolving Loans	0	0
Loans, gross	2,096	2,096
Commercial real estate | Geographic Distribution, Domestic | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	178
2020	129	383
2019	383	688
2018	689	277
2017	277	197
Prior	197	0
Revolving Loans	0	0
Loans, gross	1,675	1,723
Commercial real estate | Geographic Distribution, Domestic | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
2021	120	120
2020	49	166
2019	166	58
2018	57	0
2017	0	0
Prior	29	29
Revolving Loans	0	0
Loans, gross	$ 421	$ 373