Equity (Schedule of redeemable noncontrolling interest) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2015 USD ($)
Increase (Decrease) in Temporary Equity [Roll Forward]
Balance as of December 31, 2014	$ 810
Net income attributable to noncontrolling interest	50
Distributions payable to noncontrolling interest	(34)
Redemption value adjustment	(16)
Balance as of June 30, 2015	$ 810