Stock Compensation Plans - Nonvested Share Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation
Stock-based compensation expense recognized	$ 27	$ 16	$ 22
Tax benefit	(7)	(4)	(6)
After-tax stock-based compensation expense	20	12	16
Cash payments to settle SARs	0	1	1
Cash received from stock option exercises	$ 2	$ 9	$ 19
Performance Share Units
Summary of Activity Related to Share-based Compensation
Unvested units, beginning of period (in shares)	333,196
Units granted (in shares)	453,795
Units vested (in shares)	(123,681)
Units forfeited (in shares)	(75,310)
Unvested units, end of period (in shares)	588,000	333,196
Weighted Average Grant Date Fair Value Related to Share-based Compensation
Unvested units, beginning of period (in dollars per share)	$ 32.30
Units granted (in dollars per share)	18.01
Units vested (in dollars per share)	36.78
Units forfeited (in dollars per share)	27.24
Unvested units, end of period (in dollars per share)	$ 20.98	$ 32.30
Restricted Stock Units
Summary of Activity Related to Share-based Compensation
Unvested units, beginning of period (in shares)	1,388,433
Units granted (in shares)	1,883,570
Units vested (in shares)	(280,593)
Units forfeited (in shares)	(256,935)
Unvested units, end of period (in shares)	2,734,475	1,388,433
Weighted Average Grant Date Fair Value Related to Share-based Compensation
Unvested units, beginning of period (in dollars per share)	$ 29.81
Units granted (in dollars per share)	19.05
Units vested (in dollars per share)	29.64
Units forfeited (in dollars per share)	25.49
Unvested units, end of period (in dollars per share)	$ 23.21	$ 29.81