Derivative Instruments - Summary of Gross Principal Notional Outstanding for CDS Contracts (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Variable Interest Entity [Member] | Interest Rate Swap [Member]
Ambac Rating
Derivative, Notional Amount	$ 1,221	$ 1,233
Variable Interest Entity [Member] | Interest Rate Swap One [Member]
Ambac Rating
Derivative, Notional Amount	1,069	1,151
Variable Interest Entity [Member] | Currency Swaps [Member]
Ambac Rating
Derivative, Notional Amount	272	308
Other Credit Derivatives [Member]
Ambac Rating
Derivative, Notional Amount	$ 201	$ 257