Investments (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net Investment Income [Line Items]
Subtotal	$ 790	$ 757
Less: Investment expenses	42	42
Subtotal , net	792	759
Securities Investment
Net Investment Income [Line Items]
Subtotal	832	799
Fixed maturity securities
Net Investment Income [Line Items]
Subtotal	612	592
Equity securities
Net Investment Income [Line Items]
Subtotal	2	2
Mortgage loans
Net Investment Income [Line Items]
Subtotal	117	108
Policy loans
Net Investment Income [Line Items]
Subtotal	10	12
Real estate joint ventures
Net Investment Income [Line Items]
Subtotal	14	12
Other limited partnership interests
Net Investment Income [Line Items]
Subtotal	65	57
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Subtotal	5	8
Other
Net Investment Income [Line Items]
Subtotal	7	8
FVO CSEs — interest income — commercial mortgage loans | Consolidated Securitization Entities
Net Investment Income [Line Items]
Subtotal	$ 2	$ 2