Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Schedule of Capitalization, Equity [Line Items]
Common Stock, Shares Authorized	2,000,000,000		2,000,000,000		1,500,000,000
Common Stock, Par Value (usd per share)	$ 0.01		$ 0.01		$ 0.01
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Schedule of Capitalization, Equity [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 8	$ 7	$ 25	$ 21
5.75% Cumulative Convertible Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Dividend Rate, Percentage			5.75%
5.75% Cumulative Convertible Preferred Stock Series A [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Dividend Rate, Percentage			5.75%
4.50% Cumulative Convertible Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Dividend Rate, Percentage			4.50%
5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Dividend Rate, Percentage			5.00%