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, 2016 USD ($) $ / shares shares
Shares Subject to Options (in shares)
Outstanding as of beginning of the period | shares	9,322
Granted | shares	441
Exercised | shares	(2,091)
Forfeited | shares	(88)
Expired | shares	(599)
Outstanding as of end of the period | shares	6,985
Exercisable as of end of the period | shares	5,955
Weighted- Average Exercise Price (in dollars per share)
Outstanding as of beginning of the period | $ / shares	$ 53.98
Granted | $ / shares	63.73
Exercised | $ / shares	64.61
Forfeited | $ / shares	86.29
Expired | $ / shares	88.64
Outstanding as of end of the period | $ / shares	48.03
Exercisable as of end of the period | $ / shares	$ 44.34
Weighted-Average Remaining Contractual Term, Outstanding at end of period, years	4 years
Weighted-Average Remaining contractual Term Exercisable, at end of period years	3 years 2 months
Aggregate Intrinsic Value, Outstanding, at end of period | $	$ 274
Aggregate Intrinsic Value, Exercisable, at end of period | $	$ 255