Fair Value of Assets and Liabilities (Nonrecurring Fair Value Measurements) (Details) - Fair Value, Measurements, Nonrecurring - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Commercial mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized investment gains (losses) net	$ 2	$ (12)	$ (2)
Carrying value after measurement as of period end	15	47
Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized investment gains (losses) net	11	10	$ 7
Carrying value after measurement as of period end	$ 87	$ 73