Securities - Fair Value of Investments with Continuous Unrealized Loss Position (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Available-for-sale:
Less than 12 months, Fair value	$ 11,037,000,000	$ 23,012,000,000
Less than 12 months, Unrealized losses	56,000,000	92,000,000
12 months or more, Fair value	3,755,000,000	10,774,000,000
12 months or more, Unrealized losses	79,000,000	146,000,000
Total, Fair value	14,792,000,000	33,786,000,000
Total, Unrealized losses	135,000,000	238,000,000
AOCI, transfers from AFS to HTM Securities, gross unrealized losses, greater than 12 months	49,000,000	65,000,000
AOCI, transfers from AFS to HTM Securities, gross unrealized losses, less than 12 months	0	0
Grantor Trust
Available-for-sale:
Less than 12 months, Fair value	370,000,000
Agency RMBS
Available-for-sale:
Less than 12 months, Fair value	1,126,000,000	8,373,000,000
Less than 12 months, Unrealized losses	3,000,000	33,000,000
12 months or more, Fair value	2,102,000,000	5,912,000,000
12 months or more, Unrealized losses	52,000,000	110,000,000
Total, Fair value	3,228,000,000	14,285,000,000
Total, Unrealized losses	55,000,000	143,000,000
U.S. Treasury
Available-for-sale:
Less than 12 months, Fair value	1,041,000,000	1,976,000,000
Less than 12 months, Unrealized losses	1,000,000	16,000,000
12 months or more, Fair value	0	766,000,000
12 months or more, Unrealized losses	0	4,000,000
Total, Fair value	1,041,000,000	2,742,000,000
Total, Unrealized losses	1,000,000	20,000,000
Sovereign debt/sovereign guaranteed
Available-for-sale:
Less than 12 months, Fair value	1,069,000,000	4,045,000,000
Less than 12 months, Unrealized losses	1,000,000	10,000,000
12 months or more, Fair value	119,000,000	225,000,000
12 months or more, Unrealized losses	0	1,000,000
Total, Fair value	1,188,000,000	4,270,000,000
Total, Unrealized losses	1,000,000	11,000,000
Agency commercial mortgage-backed securities (“MBS”)
Available-for-sale:
Less than 12 months, Fair value	566,000,000	1,960,000,000
Less than 12 months, Unrealized losses	1,000,000	12,000,000
12 months or more, Fair value	306,000,000	775,000,000
12 months or more, Unrealized losses	2,000,000	5,000,000
Total, Fair value	872,000,000	2,735,000,000
Total, Unrealized losses	3,000,000	17,000,000
Foreign covered bonds
Available-for-sale:
Less than 12 months, Fair value		1,009,000,000
Less than 12 months, Unrealized losses		4,000,000
12 months or more, Fair value		690,000,000
12 months or more, Unrealized losses		3,000,000
Total, Fair value		1,699,000,000
Total, Unrealized losses		7,000,000
Supranational
Available-for-sale:
Less than 12 months, Fair value	1,583,000,000	1,336,000,000
Less than 12 months, Unrealized losses	1,000,000	6,000,000
12 months or more, Fair value	127,000,000	360,000,000
12 months or more, Unrealized losses	0	0
Total, Fair value	1,710,000,000	1,696,000,000
Total, Unrealized losses	1,000,000	6,000,000
Collateralized loan obligations (“CLOs”)
Available-for-sale:
Less than 12 months, Fair value	3,449,000,000	1,066,000,000
Less than 12 months, Unrealized losses	31,000,000	2,000,000
12 months or more, Fair value	579,000,000	1,499,000,000
12 months or more, Unrealized losses	13,000,000	14,000,000
Total, Fair value	4,028,000,000	2,565,000,000
Total, Unrealized losses	44,000,000	16,000,000
Foreign government agencies
Available-for-sale:
Less than 12 months, Fair value		1,706,000,000
Less than 12 months, Unrealized losses		2,000,000
12 months or more, Fair value		47,000,000
12 months or more, Unrealized losses		0
Total, Fair value		1,753,000,000
Total, Unrealized losses		2,000,000
U.S. government agencies
Available-for-sale:
Less than 12 months, Fair value	99,000,000	377,000,000
Less than 12 months, Unrealized losses	2,000,000	2,000,000
12 months or more, Fair value	0	0
12 months or more, Unrealized losses	0	0
Total, Fair value	99,000,000	377,000,000
Total, Unrealized losses	2,000,000	2,000,000
Other ABS
Available-for-sale:
Less than 12 months, Fair value	675,000,000	456,000,000
Less than 12 months, Unrealized losses	2,000,000	3,000,000
12 months or more, Fair value	229,000,000	305,000,000
12 months or more, Unrealized losses	2,000,000	2,000,000
Total, Fair value	904,000,000	761,000,000
Total, Unrealized losses	4,000,000	5,000,000
Non-agency commercial MBS
Available-for-sale:
Less than 12 months, Fair value	358,000,000	525,000,000
Less than 12 months, Unrealized losses	6,000,000	2,000,000
12 months or more, Fair value	194,000,000	45,000,000
12 months or more, Unrealized losses	4,000,000	0
Total, Fair value	552,000,000	570,000,000
Total, Unrealized losses	10,000,000	2,000,000
Non-agency RMBS
Available-for-sale:
Less than 12 months, Fair value	636,000,000	101,000,000
Less than 12 months, Unrealized losses	3,000,000	0
12 months or more, Fair value	97,000,000	113,000,000
12 months or more, Unrealized losses	6,000,000	7,000,000
Total, Fair value	733,000,000	214,000,000
Total, Unrealized losses	9,000,000	7,000,000
Non-agency RMBS | Grantor Trust
Available-for-sale:
Less than 12 months, Fair value	22,000,000	2,000,000
Less than 12 months, Unrealized losses	1,000,000	1,000,000
12 months or more, Fair value	1,000,000	2,000,000
12 months or more, Unrealized losses	1,000,000	1,000,000
State and political subdivisions
Available-for-sale:
Less than 12 months, Fair value	262,000,000	0
Less than 12 months, Unrealized losses	4,000,000	0
12 months or more, Fair value	2,000,000	16,000,000
12 months or more, Unrealized losses	0	0
Total, Fair value	264,000,000	16,000,000
Total, Unrealized losses	4,000,000	0
Corporate bonds
Available-for-sale:
Less than 12 months, Fair value		82,000,000
Less than 12 months, Unrealized losses		0
12 months or more, Fair value		21,000,000
12 months or more, Unrealized losses		0
Total, Fair value		103,000,000
Total, Unrealized losses		$ 0
Corporate Bond Securities
Available-for-sale:
Less than 12 months, Fair value	173,000,000
Less than 12 months, Unrealized losses	1,000,000
12 months or more, Fair value	0
12 months or more, Unrealized losses	0
Total, Fair value	173,000,000
Total, Unrealized losses	$ 1,000,000