Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Available-for-sale Debt Securities, Amortized Cost Basis	$ 53,908	$ 53,805
Available-for-sale Equity Securities, Amortized Cost Basis	1,135	1,020
Available-for-sale Securities, Equity Securities	$ 1,223	$ 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	33,726,771	28,974,069
Commercial Loan [Member]
Allowance for Loan and Lease Losses, Real Estate	$ 19	$ 19
Fixed Maturities [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	0	0
Equity Securities [Member]
Available-for-sale Equity Securities, Amortized Cost Basis	124
Available-for-sale Securities, Equity Securities	123	0
Partnership Interest [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	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	5	5
Equity Securities [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 0	$ 0