Investments (AFS Unrealized Losses) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 9,737	$ 2,556
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(94)	(8)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4,274	4,484
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(36)	(19)
Debt Securities, Available-for-sale, Unrealized Loss Position	14,011	7,040
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(130)	(27)
U.S. obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	998	196
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(15)	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	818	706
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(12)	(1)
Debt Securities, Available-for-sale, Unrealized Loss Position	1,816	902
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(27)	(1)
GSE obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	326
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(16)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position	326
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(16)
State or local housing agency obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	210	57
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	314	344
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	(5)
Debt Securities, Available-for-sale, Unrealized Loss Position	524	401
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(1)	(5)
Other Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	128
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position	128
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(1)
Non-mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,662	253
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(32)	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,132	1,050
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(13)	(6)
Debt Securities, Available-for-sale, Unrealized Loss Position	2,794	1,303
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(45)	(6)
Mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	8,075	2,303
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(62)	(8)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	3,142	3,434
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(23)	(13)
Debt Securities, Available-for-sale, Unrealized Loss Position	11,217	5,737
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(85)	(21)
Multifamily [Member] \| Mortgage-backed securities, GSE [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	4,811	2,001
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(42)	(8)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,486	2,766
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(14)	(10)
Debt Securities, Available-for-sale, Unrealized Loss Position	7,297	4,767
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(56)	(18)
Single Family [Member] \| U.S. obligations MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	3,052	169
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(19)	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	558	564
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(7)	(2)
Debt Securities, Available-for-sale, Unrealized Loss Position	3,610	733
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(26)	(2)
Single Family [Member] \| Mortgage-backed securities, GSE [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	212	133
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1)	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	98	104
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2)	(1)
Debt Securities, Available-for-sale, Unrealized Loss Position	310	237
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (3)	$ (1)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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