Background and Basis of Presentation (Share Repurchase Table) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
3 Months Ended | 9 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
Dec. 31, 2015 |
|
| Organization, Consolidation and Presentation of Financial Statements [Abstract] | |||||
| Repurchase of common stock (shares) | 2.6 | 1.2 | 8.1 | 10.0 | |
| Repurchases of common stock, value | $ 171 | $ 63 | $ 512 | $ 518 | $ 554 |
| Average price of repurchased shares, per share (usd per share) | $ 66.23 | $ 50.39 | $ 63.28 | $ 51.47 | |