Acquired Property, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Acquired Property [Roll Forward]
Beginning balance - Acquired property	$ 7,481	$ 11,442	$ 12,307
Additions	6,076	9,382	13,100
Disposals	(8,724)	(13,343)	(13,965)
Ending balance - Acquired property	4,833	7,481	11,442
Valuation allowance	(344)	(715)	(824)
Acquired property, net	4,489	6,766	10,618
Carrying amount of acquired held-for-use, net	$ 55	$ 85	$ 135