Investments in Securities - Available-for-sale Securities 1 (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	$ 506	$ 584
Allowance for Credit Losses	(2)	(2)
Gross Unrealized Gains in AOCI	13	11
Gross Unrealized Losses in AOCI	(25)	(29)
Total Fair Value	492	564
Agency securities
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	375	405
Allowance for Credit Losses	0	0
Gross Unrealized Gains in AOCI	2	1
Gross Unrealized Losses in AOCI	(25)	(29)
Total Fair Value	352	377
Other mortgage-related securities
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	131	179
Allowance for Credit Losses	(2)	(2)
Gross Unrealized Gains in AOCI	11	10
Gross Unrealized Losses in AOCI	0	0
Total Fair Value	$ 140	$ 187