Equity - Rollforward of Common Stock (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Common Stock [Roll Forward]
Common stock shares, beginning balance	795,000,000
Common stock shares, ending balance	795,000,000	795,000,000
Common Stock [Member]
Increase (Decrease) in Common Stock [Roll Forward]
Common stock shares, beginning balance	794,645,310	798,258,172	818,702,936
Exercise of stock options	233,804	688,743	1,955,108
Issuance of restricted stock	61,546	49,438	31,137
Vesting of restricted stock units	28,750	34,750	29,541
Forfeiture of unvested restricted stock	(9,318)	(2,000)	(8,675)
Repurchase of common stock		(4,383,793)	(22,451,875)
Common stock shares, ending balance	794,960,092	794,645,310	798,258,172