Stock-Based Compensation Plans - Summary of Stock Options Activity (Details) - Amended and Restated 2004 Stock Incentive Plan $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares
Shares Subject to Options (in shares)
Outstanding as of beginning of the period | shares	10,538
Granted | shares	466
Exercised | shares	(1,029)
Forfeited | shares	(49)
Expired | shares	(604)
Outstanding as of end of the period | shares	9,322
Exercisable as of end of the period | shares	8,054
Weighted- Average Exercise Price (in dollars per share)
Outstanding as of beginning of the period | $ / shares	$ 55.87
Granted | $ / shares	74.96
Exercised | $ / shares	61.95
Forfeited | $ / shares	87.98
Expired | $ / shares	86.74
Outstanding as of end of the period | $ / shares	53.98
Exercisable as of end of the period | $ / shares	$ 51.82
Weighted-Average Remaining Contractual Term, Outstanding at end of period, years	3 years 8 months
Weighted-Average Remaining contractual Term Exercisable, at end of period years	2 years 11 months
Aggregate Intrinsic Value, Outstanding, at end of period | $	$ 188
Aggregate Intrinsic Value, Exercisable, at end of period | $	$ 181