Share-Based Compensation - Summary of Non-qualified Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Weighted- Average Exercise Price
Income tax benefit	$ 10,000,000	$ 11,000,000	$ 9,000,000
Non-qualified Options
Non-qualified Options
Shares, Outstanding at beginning of year	15,705	154,551	204,434
Shares Granted	0	0	0
Shares, Exercised	(15,705)	(132,905)	(47,393)
Shares, Forfeited	0	0	0
Shares, Expired	0	(5,941)	(2,490)
Shares, Outstanding at end of year	0	15,705	154,551
Shares, Exercisable at end of period	0	15,705	154,551
Weighted- Average Exercise Price
Outstanding at beginning of year (in USD per share)	$ 26.34	$ 35.96	$ 36.66
Granted (in USD per share)	0.00	0.00	0.00
Exercised (in USD per share)	26.34	36.86	38.60
Forfeited (in USD per share)	0.00	0.00	0.00
Expired (in USD per share)	0.00	41.25	43.35
Outstanding at end of year (in USD per share)	0.00	26.34	35.96
Exercisable at end of year (in USD per share)	$ 0.00	$ 26.34	$ 35.96
Options outstanding	$ 0
Intrinsic value for options exercised	$ 2,000,000	$ 8,000,000	$ 2,000,000
Options vested in period	0	0	0
Cash received from the exercise of options	$ 1,000,000	$ 5,000,000	$ 2,000,000
Income tax benefit	$ 2,000,000	$ 2,000,000	$ 1,000,000