Investments Summary of AFS Securities with Unrealized Losses (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less Than 12 Months: Estimated Fair Value	$ 9,195	$ 2,723
Less Than 12 Months: Unrealized Losses	278	9
12 Months or More: Estimated Fair Value	402	824
12 Months or More: Unrealized Losses	40	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	9,597	3,547
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	318	22
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less Than 12 Months: Estimated Fair Value	104
Less Than 12 Months: Unrealized Losses	0
12 Months or More: Estimated Fair Value	0
12 Months or More: Unrealized Losses	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	104
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0
Total MBS
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less Than 12 Months: Estimated Fair Value	9,091
Less Than 12 Months: Unrealized Losses	278
12 Months or More: Estimated Fair Value	402
12 Months or More: Unrealized Losses	40
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	9,493
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	318
MBS – GSEs – multifamily: | MBS - GSEs
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less Than 12 Months: Estimated Fair Value	8,235	2,644
Less Than 12 Months: Unrealized Losses	240	9
12 Months or More: Estimated Fair Value	235	623
12 Months or More: Unrealized Losses	12	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	8,470	3,267
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	252	13
Freddie Mac | MBS – GSEs – multifamily: | MBS - GSEs
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less Than 12 Months: Estimated Fair Value	833	211
Less Than 12 Months: Unrealized Losses	24	0
12 Months or More: Estimated Fair Value	0	0
12 Months or More: Unrealized Losses	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	833	211
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	24	0
Fannie Mae | MBS – GSEs – multifamily: | MBS - GSEs
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less Than 12 Months: Estimated Fair Value	7,402	2,433
Less Than 12 Months: Unrealized Losses	216	9
12 Months or More: Estimated Fair Value	235	623
12 Months or More: Unrealized Losses	12	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	7,637	3,056
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	228	13
PLRMBS | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less Than 12 Months: Estimated Fair Value	856	79
Less Than 12 Months: Unrealized Losses	38	0
12 Months or More: Estimated Fair Value	167	201
12 Months or More: Unrealized Losses	28	9
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,023	280
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	66	9
Prime | PLRMBS | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less Than 12 Months: Estimated Fair Value	109	4
Less Than 12 Months: Unrealized Losses	1	0
12 Months or More: Estimated Fair Value	6	8
12 Months or More: Unrealized Losses	1	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	115	12
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2	0
Alt-A | PLRMBS | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less Than 12 Months: Estimated Fair Value	747	75
Less Than 12 Months: Unrealized Losses	37	0
12 Months or More: Estimated Fair Value	161	193
12 Months or More: Unrealized Losses	27	9
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	908	268
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 64	$ 9