Stock-Based Compensation - Summary of PBUs Granted (Details) - PBUs - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total PBUs Granted	333,800,000	1,350,750,000	2,493,333,000
PBUs Settled in Common Stock	333,800,000	560,670,000	954,583,000
PBUs Settled in Cash	0	790,080,000	1,538,750,000