Available-for-Sale Securities (Unrealized Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 2,556	$ 4,744
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(8)	(10)
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	4,484	1,824
Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(19)	(15)
Continuous Unrealized Loss Position, Fair Value	7,040	6,568
Continuous Unrealized Loss Position, Unrealized Losses	(27)	(25)
U.S. Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	196	533
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	(1)
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	706	311
Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(1)	(2)
Continuous Unrealized Loss Position, Fair Value	902	844
Continuous Unrealized Loss Position, Unrealized Losses	(1)	(3)
State or Local Housing Agency Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	57	211
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	344	586
Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(5)	(6)
Continuous Unrealized Loss Position, Fair Value	401	797
Continuous Unrealized Loss Position, Unrealized Losses	(5)	(6)
Non-Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	253	744
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	(1)
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	1,050	897
Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(6)	(8)
Continuous Unrealized Loss Position, Fair Value	1,303	1,641
Continuous Unrealized Loss Position, Unrealized Losses	(6)	(9)
Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	2,303	4,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(8)	(9)
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	3,434	927
Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(13)	(7)
Continuous Unrealized Loss Position, Fair Value	5,737	4,927
Continuous Unrealized Loss Position, Unrealized Losses	(21)	(16)
Single Family [Member] | U.S. Obligations MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	169	646
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	(1)
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	564	0
Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(2)	0
Continuous Unrealized Loss Position, Fair Value	733	646
Continuous Unrealized Loss Position, Unrealized Losses	(2)	(1)
Single Family [Member] | GSE MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	133	115
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	104	209
Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(1)	(4)
Continuous Unrealized Loss Position, Fair Value	237	324
Continuous Unrealized Loss Position, Unrealized Losses	(1)	(4)
Multifamily [Member] | GSE MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	2,001	3,239
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(8)	(8)
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	2,766	718
Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(10)	(3)
Continuous Unrealized Loss Position, Fair Value	4,767	3,957
Continuous Unrealized Loss Position, Unrealized Losses	$ (18)	$ (11)