Reinsurance (Effect of Reinsurance on Net Premiums and Claims and Other Policy Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Premiums Earned, Net [Abstract]
Direct Premiums Earned	$ 33.0	$ 58.0	$ 76.0
Assumed Premiums Earned	13,348.0	12,583.0	12,150.0
Ceded Premiums Earned	(868.0)	(947.0)	(929.0)
Net premiums	12,513.0	11,694.0	11,297.0
Policyholder Benefits and Claims Incurred, Net [Abstract]
Policyholder Benefits and Claims Incurred, Direct	37.0	97.0	113.0
Policyholder Benefits and Claims Incurred, Assumed	13,725.0	11,931.0	11,404.0
Policyholder Benefits and Claims Incurred, Ceded	(986.0)	(953.0)	(1,320.0)
Claims and other policy benefits	$ 12,776.0	$ 11,075.0	$ 10,197.0