Acquired Property, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Acquired Property [Roll Forward]
Beginning balance - Acquired property	$ 5,928	$ 9,199	$ 7,481	$ 11,442
Additions	1,391	2,236	4,876	7,602
Disposals	(1,906)	(3,125)	(6,944)	(10,734)
Ending balance - Acquired property	5,413	8,310	5,413	8,310
Valuation allowance	(372)	(619)	(372)	(619)
Ending balance - Acquired property, net	$ 5,041	$ 7,691	$ 5,041	$ 7,691	$ 6,766