Equity - Rollforward of Common Stock (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Common Stock [Roll Forward]
Common stock shares, beginning balance	789,000,000
Common stock shares, ending balance	775,000,000	789,000,000
Common Stock [Member]
Increase (Decrease) in Common Stock [Roll Forward]
Common stock shares, beginning balance	789,484,987	794,960,092	794,645,310
Exercise of stock options	1,007,551	617,612	233,804
Issuance of restricted stock	10,296	37,270	61,546
Vesting of restricted stock units	5,000	64,150	28,750
Forfeiture of unvested restricted stock			(9,318)
Repurchase of common stock	(15,044,620)	(6,194,137)
Common stock shares, ending balance	775,463,214	789,484,987	794,960,092