Parent Company Stock-Based Compensation - RSUs Granted Employees and Key Executive Officers Under Parent Company Stock Based Compensation Programs (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares outstanding
Outstanding at beginning of period (in shares)	2,827,000
Granted (in shares)	915,000	0
Settled (in shares)	(701,000)
Forfeited or expired (in shares)	(168,000)
Outstanding at end of period (in shares)	2,873,000	2,827,000
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share)	$ 25.37
Granted (in dollars per share)	32.90
Forfeited or expired (in dollars per share)	36.56
Settled (in dollars per share)	11.93
Outstanding at end of period (in dollars per share)	$ 28.44	$ 25.37
Weighted-Average Remaining Contractual Term
RSUs at beginning of period (in years)	1 year 4 months 24 days	1 year 8 months 12 days
RSU's vested and payable at end of period (in years)	1 year 10 months 24 days
RSUs unvested and expected to vest at end of period (in shares)	1,837,000
RSUs vested and payable at end of period (in shares)	949,000
RSUs unvested and expected to vest at end of period (in dollars per share)	$ 34.51
RSUs vested and payable at end of period (in dollars per share)	$ 16.71