Investments in Securities - Available-for-sale Securities 1 (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	$ 616	$ 714
Allowance for Credit Losses	(2)	(3)
Gross Unrealized Gains in AOCI	9	8
Gross Unrealized Losses in AOCI	(39)	(23)
Total Fair Value	584	696
Agency securities
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	414	445
Allowance for Credit Losses	0	0
Gross Unrealized Gains in AOCI	0	3
Gross Unrealized Losses in AOCI	(38)	(22)
Total Fair Value	376	426
Other mortgage-related securities
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	202	269
Allowance for Credit Losses	(2)	(3)
Gross Unrealized Gains in AOCI	9	5
Gross Unrealized Losses in AOCI	(1)	(1)
Total Fair Value	$ 208	$ 270