Stock-based Compensation - Options Vested and Expected to Vest (Details) - Long-term incentive and director compensation plans - Employee Stock Option $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of outstanding shares, vested and expected to vest (in shares) | shares	55,421,103	[1]
Weighted-average remaining contractual life, vested and expected to vest (in years)	6 years 4 months 24 days	[1]
Weighted-average exercise price per share, vested and expected to vest (in dollars per share) | $ / shares	$ 37.17	[1]
Intrinsic value, vested and expected to vest (millions of dollars) | $	$ 978	[1]
Outstanding options exercisable (in shares) | shares	26,840,082
Weighted-average remaining contractual life, options exercisable	4 years 7 months 6 days
Weighted-average exercise price per share, options exercisable (in dollars per share) | $ / shares	$ 29.35
Intrinsic value, options exercisable (millions of dollars) | $	$ 683

[1] Includes effects of expected forfeitures of approximately 1 million shares. Excluding the effects of expected forfeitures, the aggregate intrinsic value of stock options outstanding was $986 million.