Derivative Instruments - Summary of Gross Principal Notional Outstanding for CDS Contracts (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Other Credit Derivatives [Member]
Ambac Rating
Derivative, Notional Amount	$ 0	$ 201
Variable Interest Entity [Member] | Interest Rate Swap [Member]
Ambac Rating
Derivative, Notional Amount	1,573	1,221
Variable Interest Entity [Member] | Interest Rate Swap One [Member]
Ambac Rating
Derivative, Notional Amount	887	1,069
Variable Interest Entity [Member] | Currency Swaps [Member]
Ambac Rating
Derivative, Notional Amount	$ 176	$ 272