Investments in Securities - Available-for-sale Securities 1 (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	$ 547	$ 584
Allowance for Credit Losses	(2)	(2)
Gross Unrealized Gains in AOCI	19	11
Gross Unrealized Losses in AOCI	(29)	(29)
Total Fair Value	535	564
Agency securities
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	395	405
Allowance for Credit Losses	0	0
Gross Unrealized Gains in AOCI	1	1
Gross Unrealized Losses in AOCI	(29)	(29)
Total Fair Value	367	377
Other mortgage-related securities
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	152	179
Allowance for Credit Losses	(2)	(2)
Gross Unrealized Gains in AOCI	18	10
Gross Unrealized Losses in AOCI	0	0
Total Fair Value	$ 168	$ 187