Fair Value of Assets and Liabilities (Nonrecurring Fair Value Measurements) (Details) - Fair Value, Measurements, Nonrecurring - Level 3 - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Commercial Mortgage Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized investment gains (losses) net	$ 0	$ 3	$ 0	$ 0
Carrying value after measurement as of period end	0		0		$ 0
Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized investment gains (losses) net	0	5	(6)	(24)
Carrying value after measurement as of period end	281		281		307
Investment real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized investment gains (losses) net	0	$ 0	(9)	$ 0
Carrying value after measurement as of period end	$ 17		$ 17		$ 31