Income Taxes Summary of Gross Unrecognized Income Tax Benefits (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Summary of Gross Unrecognized Income Tax Benefits [Abstract] | |||
| Balance at January 1 | $ 493 | $ 479 | $ 444 |
| Increases and decreases as a result of positions taken during prior years | |||
| Transfers from valuation allowances | 0 | (3) | 13 |
| Other increases, including currency translation | 34 | 37 | 7 |
| Other decreases, including currency translation | (34) | (3) | (7) |
| Balances related to acquired businesses | (1) | (3) | 2 |
| Increases as a result of positions taken during the current year | 109 | 65 | 35 |
| Decreases relating to settlements with tax authorities | 0 | (51) | (6) |
| Decreases as a result of a lapse of the applicable statute of limitations | (17) | (28) | (9) |
| Balance at December 31 | $ 584 | $ 493 | $ 479 |