Securities - Fair Value of Investments with Continuous Unrealized Loss Position (Details) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Available-for-sale:
Less than 12 months, Fair value	$ 12,385,000,000	$ 23,012,000,000
Less than 12 months, Unrealized losses	110,000,000	92,000,000
12 months or more, Fair value	7,919,000,000	10,774,000,000
12 months or more, Unrealized losses	113,000,000	146,000,000
Total, Fair value	20,304,000,000	33,786,000,000
Total, Unrealized losses	223,000,000	238,000,000
AOCI, transfers from AFS to HTM Securities, gross unrealized losses, greater than 12 months	55,000,000	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	530,000,000
Agency RMBS
Available-for-sale:
Less than 12 months, Fair value	2,809,000,000	8,373,000,000
Less than 12 months, Unrealized losses	5,000,000	33,000,000
12 months or more, Fair value	6,030,000,000	5,912,000,000
12 months or more, Unrealized losses	79,000,000	110,000,000
Total, Fair value	8,839,000,000	14,285,000,000
Total, Unrealized losses	84,000,000	143,000,000
U.S. Treasury
Available-for-sale:
Less than 12 months, Fair value		1,976,000,000
Less than 12 months, Unrealized losses		16,000,000
12 months or more, Fair value		766,000,000
12 months or more, Unrealized losses		4,000,000
Total, Fair value		2,742,000,000
Total, Unrealized losses		20,000,000
Sovereign debt/sovereign guaranteed
Available-for-sale:
Less than 12 months, Fair value	1,952,000,000	4,045,000,000
Less than 12 months, Unrealized losses	2,000,000	10,000,000
12 months or more, Fair value	110,000,000	225,000,000
12 months or more, Unrealized losses	0	1,000,000
Total, Fair value	2,062,000,000	4,270,000,000
Total, Unrealized losses	2,000,000	11,000,000
Agency commercial mortgage-backed securities (“MBS”)
Available-for-sale:
Less than 12 months, Fair value	266,000,000	1,960,000,000
Less than 12 months, Unrealized losses	0	12,000,000
12 months or more, Fair value	350,000,000	775,000,000
12 months or more, Unrealized losses	2,000,000	5,000,000
Total, Fair value	616,000,000	2,735,000,000
Total, Unrealized losses	2,000,000	17,000,000
Foreign covered bonds
Available-for-sale:
Less than 12 months, Fair value	1,003,000,000	1,009,000,000
Less than 12 months, Unrealized losses	2,000,000	4,000,000
12 months or more, Fair value	281,000,000	690,000,000
12 months or more, Unrealized losses	1,000,000	3,000,000
Total, Fair value	1,284,000,000	1,699,000,000
Total, Unrealized losses	3,000,000	7,000,000
Supranational
Available-for-sale:
Less than 12 months, Fair value	931,000,000	1,336,000,000
Less than 12 months, Unrealized losses	1,000,000	6,000,000
12 months or more, Fair value	233,000,000	360,000,000
12 months or more, Unrealized losses	0	0
Total, Fair value	1,164,000,000	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	3,522,000,000	1,066,000,000
Less than 12 months, Unrealized losses	68,000,000	2,000,000
12 months or more, Fair value	575,000,000	1,499,000,000
12 months or more, Unrealized losses	19,000,000	14,000,000
Total, Fair value	4,097,000,000	2,565,000,000
Total, Unrealized losses	87,000,000	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	79,000,000	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	79,000,000	377,000,000
Total, Unrealized losses	2,000,000	2,000,000
Other ABS
Available-for-sale:
Less than 12 months, Fair value	760,000,000	456,000,000
Less than 12 months, Unrealized losses	6,000,000	3,000,000
12 months or more, Fair value	203,000,000	305,000,000
12 months or more, Unrealized losses	4,000,000	2,000,000
Total, Fair value	963,000,000	761,000,000
Total, Unrealized losses	10,000,000	5,000,000
Non-agency commercial MBS
Available-for-sale:
Less than 12 months, Fair value	476,000,000	525,000,000
Less than 12 months, Unrealized losses	15,000,000	2,000,000
12 months or more, Fair value	39,000,000	45,000,000
12 months or more, Unrealized losses	1,000,000	0
Total, Fair value	515,000,000	570,000,000
Total, Unrealized losses	16,000,000	2,000,000
Non-agency RMBS
Available-for-sale:
Less than 12 months, Fair value	508,000,000	101,000,000
Less than 12 months, Unrealized losses	7,000,000	0
12 months or more, Fair value	96,000,000	113,000,000
12 months or more, Unrealized losses	7,000,000	7,000,000
Total, Fair value	604,000,000	214,000,000
Total, Unrealized losses	14,000,000	7,000,000
Non-agency RMBS | Grantor Trust
Available-for-sale:
Less than 12 months, Fair value	42,000,000	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	79,000,000	0
Less than 12 months, Unrealized losses	2,000,000	0
12 months or more, Fair value	2,000,000	16,000,000
12 months or more, Unrealized losses	0	0
Total, Fair value	81,000,000	16,000,000
Total, Unrealized losses	$ 2,000,000	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