Stock Compensation Plans - Options (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Summary of Stock Options Outstanding Activity
Options outstanding, beginning of period (in shares)		10,350,633
Options granted (in shares)		802,871
Options exercised (in shares)		(3,028,112)
Options expired (in shares)		(52,687)
Options cancelled (in shares)		(290,009)
Options outstanding, end of period (in shares)		7,782,696	10,350,633
Options Weighted Average Exercise Price
Options outstanding weighted average exercise price, beginning of period		$ 16.75
Options granted weighted average exercise price		27.32
Options exercised weighted average exercise price		18.35
Options expired weighted average exercise price		17.15
Options cancelled weighted average exercise price		18.67
Options outstanding weighted average exercise price, end of period		$ 17.15	$ 16.75
Vested and expected to vest, options					7,493,529
Vested and expected to vest, options weighted average exercise price					$ 17.03
Options exercisable					5,153,908
Options exercisable, weighted average exercise price					$ 15.55
Available for grant, options					8,645,222
Options outstanding, weighted average remaining contractual term (in years)		5 years 9 months 18 days
Options vested and expected to vest, weighted average remaining contractual term (in years)		5 years 8 months 12 days
Options exercisable, weighted average remaining contractual term (in years)		4 years 8 months 12 days
Options exercised, aggregate intrinsic value		$ 40	$ 37	$ 23
Options outstanding, aggregate intrinsic value					$ 121
Options vested and expected to vest, aggregate intrinsic value					119
Options exercisable, aggregate intrinsic value					$ 89
Options outstanding (in shares)		10,350,633	10,350,633		7,782,696
Weighted average grant date fair value, stock options		$ 11.51	$ 11.48	$ 6.28
Black-Scholes model assumptions:
Expected term (years)	[1]	7 years 3 months 18 days	7 years 4 months 23 days	6 years 3 months
Interest rate	[1]	1.83%	2.10%	1.11%
Volatility	[1]	42.00%	43.45%	46.66%
Dividend yield	[1]	0.88%	0.81%	0.00%
Grant Date February 23 2015
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		719,164
Options Weighted Average Exercise Price
Options exercisable					0
Options outstanding, weighted average remaining contractual term (in years)		9 years 2 months 6 days
Options outstanding (in shares)		719,164			719,164
Options exercise price					$ 27.16
Grant Date February 24 2014
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		502,513
Options Weighted Average Exercise Price
Options exercisable					111,397
Options outstanding, weighted average remaining contractual term (in years)		8 years 2 months 12 days
Options outstanding (in shares)		502,513			502,513
Options exercise price					$ 26.44
Grant Date February 28 2013
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		1,512,308
Options Weighted Average Exercise Price
Options exercisable					695,216
Options outstanding, weighted average remaining contractual term (in years)		7 years 2 months 12 days
Options outstanding (in shares)		1,512,308			1,512,308
Options exercise price					$ 12.98
Grant Date February 27 2012
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		1,139,048
Options Weighted Average Exercise Price
Options exercisable					805,963
Options outstanding, weighted average remaining contractual term (in years)		6 years 2 months 12 days
Options outstanding (in shares)		1,139,048			1,139,048
Options exercise price					$ 12.94
Grant Date February 22 2011
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		729,512
Options Weighted Average Exercise Price
Options exercisable					729,512
Options outstanding, weighted average remaining contractual term (in years)		5 years 2 months 12 days
Options outstanding (in shares)		729,512			729,512
Options exercise price					$ 13.91
Grant Date February 23 2010
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		547,334
Options Weighted Average Exercise Price
Options exercisable					547,334
Options outstanding, weighted average remaining contractual term (in years)		4 years 2 months 12 days
Options outstanding (in shares)		547,334			547,334
Options exercise price					$ 12.74
Grant Date February 26 2009
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		489,562
Options Weighted Average Exercise Price
Options exercisable					489,562
Options outstanding, weighted average remaining contractual term (in years)		3 years 2 months 12 days
Options outstanding (in shares)		489,562			489,562
Options exercise price					$ 4.81
Grant Date February 21 2008
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		486,390
Options Weighted Average Exercise Price
Options exercisable					486,390
Options outstanding, weighted average remaining contractual term (in years)		2 years 2 months 12 days
Options outstanding (in shares)		486,390			486,390
Options exercise price					$ 26.74
Grant Date February 27 2007
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		477,584
Options Weighted Average Exercise Price
Options exercisable					477,584
Options outstanding, weighted average remaining contractual term (in years)		1 year 2 months 12 days
Options outstanding (in shares)		477,584			477,584
Options exercise price					$ 24.71
All Other Grant Dates
Summary of Stock Options Outstanding Activity
Options outstanding, end of period (in shares)		1,179,281
Options Weighted Average Exercise Price
Options outstanding weighted average exercise price, end of period		$ 18.65
Options exercisable					810,950
Options exercisable, weighted average exercise price					$ 16.63
Options outstanding, weighted average remaining contractual term (in years)		6 years 1 month 6 days
Options exercisable, weighted average remaining contractual term (in years)		5 years
Options outstanding (in shares)		1,179,281			1,179,281

[1] We review the assumptions used in our Black-Scholes model in conjunction with estimating the grant date fair value of the annual grants of options by our Board of Directors.