Insurance Contracts Financial Guarantee Insurance Contracts - Components of Loss and Loss Expense Reserves and Subrogation Recoverable (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered		$ 0
Policyholder Benefits and Claims Incurred, Ceded	$ 7	1
Subrogation recoverable	(1,714)		$ (2,092)
Claim liability reported on Balance Sheet, before reinsurance	(683)		(554)
Liability for Claims and Claims Adjustment Expense	1,067		1,570
Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables	(647)	$ (414)	(522)	$ (397)
Property and Casualty, Commercial Insurance
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Liability for Claims and Claims Adjustment Expense	36		32
Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables	36		32
Present Value of Expected Net Cash Flows- Claims and Loss Expenses [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Subrogation recoverable	52		88
Claim liability reported on Balance Sheet, before reinsurance	1,221		1,837
Liability for Claims and Claims Adjustment Expense	1,168		1,749
Present Value of Expected Net Cash Flows-Recoveries [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Subrogation recoverable	(1,766)		(2,180)
Claim liability reported on Balance Sheet, before reinsurance	(1,861)		(2,335)
Liability for Claims and Claims Adjustment Expense	(95)		(155)
Unearned Premium Reserve [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Subrogation recoverable	0		0
Claim liability reported on Balance Sheet, before reinsurance	(42)		(56)
Liability for Claims and Claims Adjustment Expense	$ (42)		$ (56)