Investments (Fair Value of Trading Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	$ 1,620	$ 1,712
Corporate Bonds [Member] | Fixed maturity AFS securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	1,335	1,360
ABS [Member] | Fixed maturity AFS securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	15	19
U.S. government bonds [Member] | Fixed maturity AFS securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	115	164
Foreign Government Bonds [Member] | Fixed maturity AFS securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	23	23
RMBS [Member] | Fixed maturity AFS securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	86	97
CMBS [Member] | Fixed maturity AFS securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	2	2
CLOs [Member] | Fixed maturity AFS securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	3	6
State and municipal bonds [Member] | Fixed maturity AFS securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	17	18
Hybrid and redeemable preferred securities [Member] | Fixed maturity AFS securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	$ 24	$ 23