Acquired Property, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Acquired Property [Roll Forward]
Beginning balance - Acquired property	$ 7,481	$ 11,442
Additions	1,837	2,935
Disposals	(2,581)	(4,029)
Ending balance - Acquired property	6,737	10,348
Valuation allowance	(549)	(830)
Ending balance - Acquired property, net	$ 6,188	$ 9,518	$ 6,766