Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale Debt Securities, Amortized Cost Basis	$ 54,800	$ 53,805
Available-for-sale Equity Securities, Amortized Cost Basis	964	1,020
Available-for-sale Securities, Equity Securities	$ 1,055	$ 1,097
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,500,000,000	1,500,000,000
Common stock, shares issued	402,923,222	402,923,222
Treasury stock, shares	40,103,642	28,974,069
Commercial Loan [Member]
Allowance for Loan and Lease Losses, Real Estate	$ 1	$ 19
Fixed Maturities [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	0	0
Equity Securities [Member]
Available-for-sale Securities, Equity Securities	0	0
Other Assets [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	0	0
Short-term Investments [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	0	0
Cash [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	0	5
Equity Securities [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	0	0
Debt Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	40,807	39,911
Partnership Interest [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 0	$ 0