Share-Based Compensation Restricted Stock (Details) - Restricted Stock Units (RSUs) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) $ / shares shares
Restricted unit activity
Non-vested at the beginning of the period (in shares) | shares	439
Granted (in shares) | shares	142
Vested (in shares) | shares	(113)
Cancelled (in shares) | shares	(11)
Non-vested at the end of the period (in shares) | shares	457
Weighted-average fair value per share
Non-vested at the beginning of the period (in dollars per share) | $ / shares	$ 69.96
Granted (in dollars per share) | $ / shares	99.82
Vested (in dollars per share) | $ / shares	66.77
Cancelled (in dollars per share) | $ / shares	72.77
Non-vested at the end of the period (in dollars per share) | $ / shares	$ 79.95
Unrecognized compensation cost | $	$ 24
Weighted-average period for amortization of unrecognized compensation cost	2 years 1 month 6 days
Minimum
Equity stock-based compensation
Vesting terms	3 years