Common Stock, Preferred Stock and Equity Plans - Restricted Stock and Restricted Stock Units and PSUs (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Stock
Restricted stock and Restricted Stock Units
Beginning of the period (in shares)	1,229
Granted (in shares)	0
Vested (in shares)	(690)
Cancelled (in shares)	(59)
End of the period (in shares)	480	1,229
Restricted stock and Restricted Stock Units, weighted-average grant-date fair value
Weighted-average grant-date fair value, as of the beginning of the period (usd per share)	$ 102.12
Weighted-average grant-date fair value, granted (usd per share)	0.00
Weighted-average grant-date fair value, vested (usd per share)	100.07
Weighted-average grant-date fair value, cancelled (usd per share)	101.55
Weighted-average grant-date fair value, as of the end of the period (usd per share)	$ 104.91	$ 102.12
Restricted stock vested in period, total fair value	$ 114.5	$ 157.0	$ 74.1
Restricted Stock Units (excluding PSUs)
Restricted stock and Restricted Stock Units
Beginning of the period (in shares)	2,011
Granted (in shares)	1,600
Vested (in shares)	(629)
Cancelled (in shares)	(265)
End of the period (in shares)	2,717	2,011
Restricted stock and Restricted Stock Units, weighted-average grant-date fair value
Weighted-average grant-date fair value, as of the beginning of the period (usd per share)	$ 109.27
Weighted-average grant-date fair value, granted (usd per share)	164.70
Weighted-average grant-date fair value, vested (usd per share)	108.02
Weighted-average grant-date fair value, cancelled (usd per share)	132.26
Weighted-average grant-date fair value, as of the end of the period (usd per share)	$ 140.10	$ 109.27
Restricted stock vested in period, total fair value	$ 104.8	$ 33.2	$ 5.3
Performance-based RSUs
Restricted stock and Restricted Stock Units
Beginning of the period (in shares)	484
Granted (in shares)	494
Vested (in shares)	(154)
Cancelled (in shares)	(65)
End of the period (in shares)	759	484
Restricted stock and Restricted Stock Units, weighted-average grant-date fair value
Weighted-average grant-date fair value, as of the beginning of the period (usd per share)	$ 87.59
Weighted-average grant-date fair value, granted (usd per share)	152.40
Weighted-average grant-date fair value, vested (usd per share)	87.13
Weighted-average grant-date fair value, cancelled (usd per share)	99.34
Weighted-average grant-date fair value, as of the end of the period (usd per share)	$ 110.50	$ 87.59
Restricted stock vested in period, total fair value	$ 23.2	$ 1.3
Potential awards, percent of target shares, minimum	0.00%
Potential awards, percent of target shares, maximum	200.00%
Performance-based RSUs | Tranche one
Restricted stock and Restricted Stock Units, weighted-average grant-date fair value
Percent of awards in tranche	50.00%
Performance period	1 year
Vesting period	3 years
Performance-based RSUs | Tranche two
Restricted stock and Restricted Stock Units, weighted-average grant-date fair value
Percent of awards in tranche	50.00%
Performance period	3 years
Vesting period	3 years