Investment Securities - Fair Value and Gross Unrealized Losses by Aging Category (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Available-for-sale securities
Less than 12 months, Fair value	$ 11,094	$ 12,133
Less than 12 months, Gross unrealized losses	91	57
12 months or more, Fair Value	3,795	4,694
12 months or more, Gross unrealized losses	26	49
Total fair value	14,889	16,827
Total gross unrealized losses	117	106
Total mortgage-backed securities
Available-for-sale securities
Less than 12 months, Fair value	2,071	3,768
Less than 12 months, Gross unrealized losses	17	25
12 months or more, Fair Value	430	391
12 months or more, Gross unrealized losses	15	17
Total fair value	2,501	4,159
Total gross unrealized losses	32	42
U.S. GSEs and government agencies
Available-for-sale securities
Total fair value	3,600	150
Residential: U.S.
Available-for-sale securities
Less than 12 months, Fair value	801	562
Less than 12 months, Gross unrealized losses	5	3
12 months or more, Fair Value	53	32
12 months or more, Gross unrealized losses	0	0
Total fair value	854	594
Total gross unrealized losses	5	3
Residential: Non-U.S.
Available-for-sale securities
Less than 12 months, Fair value	769	2,507
Less than 12 months, Gross unrealized losses	0	4
12 months or more, Fair Value	33	235
12 months or more, Gross unrealized losses	0	1
Total fair value	802	2,742
Total gross unrealized losses	0	5
Commercial
Available-for-sale securities
Less than 12 months, Fair value	501	699
Less than 12 months, Gross unrealized losses	12	18
12 months or more, Fair Value	344	124
12 months or more, Gross unrealized losses	15	16
Total fair value	845	823
Total gross unrealized losses	27	34
Obligations of U.S. states and municipalities
Available-for-sale securities
Less than 12 months, Fair value	218	49
Less than 12 months, Gross unrealized losses	5	1
12 months or more, Fair Value	0	0
12 months or more, Gross unrealized losses	0	0
Total fair value	218	49
Total gross unrealized losses	5	1
Non-U.S. government debt securities
Available-for-sale securities
Less than 12 months, Fair value	6,620	2,709
Less than 12 months, Gross unrealized losses	61	9
12 months or more, Fair Value	580	968
12 months or more, Gross unrealized losses	3	4
Total fair value	7,200	3,677
Total gross unrealized losses	64	13
Corporate debt securities
Available-for-sale securities
Less than 12 months, Fair value	52	91
Less than 12 months, Gross unrealized losses	3	3
12 months or more, Fair Value	42	5
12 months or more, Gross unrealized losses	1	0
Total fair value	94	96
Total gross unrealized losses	4	3
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Less than 12 months, Fair value	1,808	5,248
Less than 12 months, Gross unrealized losses	4	18
12 months or more, Fair Value	2,254	2,645
12 months or more, Gross unrealized losses	1	13
Total fair value	4,062	7,893
Total gross unrealized losses	5	31
Asset-backed securities: Other
Available-for-sale securities
Less than 12 months, Fair value	325	268
Less than 12 months, Gross unrealized losses	1	1
12 months or more, Fair Value	489	685
12 months or more, Gross unrealized losses	6	15
Total fair value	814	953
Total gross unrealized losses	$ 7	$ 16