Investment Securities - Fair Value and Gross Unrealized Losses by Aging Category (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Available-for-sale securities
Less than 12 months, Fair value	$ 38,604		$ 18,608
Less than 12 months, Gross unrealized losses	616		49
12 months or more, Fair Value	7,433		10,957
12 months or more, Gross unrealized losses	219		65
Total fair value	46,037		29,565
Total gross unrealized losses	835		114
Total mortgage-backed securities
Available-for-sale securities
Less than 12 months, Fair value	8,284		2,372
Less than 12 months, Gross unrealized losses	117		15
12 months or more, Fair Value	697		1,042
12 months or more, Gross unrealized losses	41		5
Total fair value	8,981		3,414
Total gross unrealized losses	158		20
U.S. GSEs and government agencies
Available-for-sale securities
Total fair value	750		264
Residential: U.S.
Available-for-sale securities
Less than 12 months, Fair value	2,570		1,072
Less than 12 months, Gross unrealized losses	28		3
12 months or more, Fair Value	259		423
12 months or more, Gross unrealized losses	6		3
Total fair value	2,829		1,495
Total gross unrealized losses	34		6
Residential: Non-U.S.
Available-for-sale securities
Less than 12 months, Fair value	3,764		13
Less than 12 months, Gross unrealized losses	28		0
12 months or more, Fair Value	261		420
12 months or more, Gross unrealized losses	3		1
Total fair value	4,025		433
Total gross unrealized losses	31		1
Commercial
Available-for-sale securities
Less than 12 months, Fair value	1,950		1,287
Less than 12 months, Gross unrealized losses	61		12
12 months or more, Fair Value	177		199
12 months or more, Gross unrealized losses	32		1
Total fair value	2,127		1,486
Total gross unrealized losses	93		13
Obligations of U.S. states and municipalities
Available-for-sale securities
Less than 12 months, Fair value	410		186
Less than 12 months, Gross unrealized losses	10		1
12 months or more, Fair Value	0		0
12 months or more, Gross unrealized losses	0		0
Total fair value	410		186
Total gross unrealized losses	10		1
Certificates of deposit
Available-for-sale securities
Less than 12 months, Fair value	0		77
Less than 12 months, Gross unrealized losses	0		0
12 months or more, Fair Value	0		0
12 months or more, Gross unrealized losses	0		0
Total fair value	0		77
Total gross unrealized losses	0		0
Non-U.S. government debt securities
Available-for-sale securities
Less than 12 months, Fair value	3,183		3,970
Less than 12 months, Gross unrealized losses	4		13
12 months or more, Fair Value	808		1,406
12 months or more, Gross unrealized losses	3		4
Total fair value	3,991		5,376
Total gross unrealized losses	7		17
Corporate debt securities
Available-for-sale securities
Less than 12 months, Fair value	390		0
Less than 12 months, Gross unrealized losses	6		0
12 months or more, Fair Value	0		0
12 months or more, Gross unrealized losses	0		0
Total fair value	390		0
Total gross unrealized losses	6		0
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Less than 12 months, Fair value	24,866		10,364
Less than 12 months, Gross unrealized losses	456		11
12 months or more, Fair Value	5,003		7,756
12 months or more, Gross unrealized losses	134		45
Total fair value	29,869		18,120
Total gross unrealized losses	590	$ 2,000	56
Asset-backed securities: Other
Available-for-sale securities
Less than 12 months, Fair value	1,471		1,639
Less than 12 months, Gross unrealized losses	23		9
12 months or more, Fair Value	925		753
12 months or more, Gross unrealized losses	41		11
Total fair value	2,396		2,392
Total gross unrealized losses	$ 64		$ 20