Incentive Based Compensation Plans - Stock Option Award Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Beginning of year, stock option awards (in shares)	10,330,776
Granted, stock option awards (in shares)	856,890
Exercised, stock option awards (in shares)	(1,878,836)
Canceled, stock option awards (in shares)	(3,128,823)
End of year, stock option awards (in shares)	6,180,007	10,330,776
Exercisable at end of year, stock option awards (in shares)	4,523,008
Expected to vest, stock option awards (in shares)	1,635,216
Weighted Average Exercise Price
Beginning of year, weighted average exercise price (in dollars per share)	$ 25.52
Granted, weighted average exercise price (in dollars per share)	14.52	$ 15.80	$ 7.22
Exercises, weighted average exercise price (in dollars per share)	14.02
Canceled, weighted average exercise price (in dollars per share)	31.64
End of year, weighted average exercise price (in dollars per share)	24.39	$ 25.52
Exercisable at end of year, weighted average exercise price (in dollars per share)	28.46
Expected to vest, weighted average exercise price (in dollars per share)	$ 13.25
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding at end of year, Weighted Average Remaining Contractual Term	5 years
Exercisable at end of year, Weighted Average Remaining Contractual Term	3 years
Expected to vest, Weighted Average Remaining Contractual Term	8 years
Outstanding at end of year, Average Intrinsic Value	$ 4
Exercisable at end of year, Average Intrinsic Value	1
Expected to vest, Average Intrinsic Value	3
Stock option awards, intrinsic value	13
Unrecognized compensation costs	$ 5
Unrecognized compensation costs, period for recognition	1 year