Investment Securities - Fair Value and Gross Unrealized Losses by Aging Category (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Available-for-sale securities
Less than 12 months, Fair value	$ 11,788	$ 12,133
Less than 12 months, Gross unrealized losses	40	57
12 months or more, Fair Value	1,351	4,694
12 months or more, Gross unrealized losses	15	49
Total fair value	13,139	16,827
Total gross unrealized losses	55	106
Total mortgage-backed securities
Available-for-sale securities
Less than 12 months, Fair value	456	3,768
Less than 12 months, Gross unrealized losses	5	25
12 months or more, Fair Value	394	391
12 months or more, Gross unrealized losses	6	17
Total fair value	850	4,159
Total gross unrealized losses	11	42
U.S. GSEs and government agencies
Available-for-sale securities
Total fair value	1,300	150
Residential: U.S.
Available-for-sale securities
Less than 12 months, Fair value	72	562
Less than 12 months, Gross unrealized losses	0	3
12 months or more, Fair Value	31	32
12 months or more, Gross unrealized losses	0	0
Total fair value	103	594
Total gross unrealized losses	0	3
Residential: Non-U.S.
Available-for-sale securities
Less than 12 months, Fair value	134	2,507
Less than 12 months, Gross unrealized losses	0	4
12 months or more, Fair Value	0	235
12 months or more, Gross unrealized losses	0	1
Total fair value	134	2,742
Total gross unrealized losses	0	5
Commercial
Available-for-sale securities
Less than 12 months, Fair value	250	699
Less than 12 months, Gross unrealized losses	5	18
12 months or more, Fair Value	363	124
12 months or more, Gross unrealized losses	6	16
Total fair value	613	823
Total gross unrealized losses	11	34
Obligations of U.S. states and municipalities
Available-for-sale securities
Less than 12 months, Fair value	271	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	271	49
Total gross unrealized losses	5	1
Non-U.S. government debt securities
Available-for-sale securities
Less than 12 months, Fair value	5,031	2,709
Less than 12 months, Gross unrealized losses	17	9
12 months or more, Fair Value	441	968
12 months or more, Gross unrealized losses	7	4
Total fair value	5,472	3,677
Total gross unrealized losses	24	13
Corporate debt securities
Available-for-sale securities
Less than 12 months, Fair value	149	91
Less than 12 months, Gross unrealized losses	9	3
12 months or more, Fair Value	40	5
12 months or more, Gross unrealized losses	0	0
Total fair value	189	96
Total gross unrealized losses	9	3
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Less than 12 months, Fair value	4,381	5,248
Less than 12 months, Gross unrealized losses	4	18
12 months or more, Fair Value	270	2,645
12 months or more, Gross unrealized losses	0	13
Total fair value	4,651	7,893
Total gross unrealized losses	4	31
Asset-backed securities: Other
Available-for-sale securities
Less than 12 months, Fair value	1,500	268
Less than 12 months, Gross unrealized losses	0	1
12 months or more, Fair Value	206	685
12 months or more, Gross unrealized losses	2	15
Total fair value	1,706	953
Total gross unrealized losses	$ 2	$ 16