Basis of Presentation and Significant Accounting Policies Noncontrolling Interest (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares
Stockholders' Equity Attributable to Noncontrolling Interest	$ 60	$ 60
Preferred Stock, Shares Outstanding | shares	0	0
Redeemable Noncontrolling Interest, Equity, Carrying Amount	$ 18	$ 7
Noncontrolling Interest, Increase from Subsidiary Equity Issuance		$ 7
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	(1)
Temporary Equity, Accretion to Redemption Value, Adjustment	$ 12
Ambac Assurance Corporation [Member]
Preferred Stock, Shares Outstanding | shares	5,501	5,501
Preferred Stock, Liquidation Preference, Value	$ 138	$ 138
London Interbank Offered Rate (LIBOR) [Member]
Dividend Rate on Auction Rate Preferred Shares	200