Acquisitions and Divestitures - 2016 Activity (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015		Sep. 30, 2016	Sep. 30, 2015
Business Combinations [Abstract]
Leasehold and property acquisitions	$ 51	$ 126		$ 169	$ 254	[1]
Transaction, reorganization, and separation	$ 12	$ 0	[2]	$ 36	$ 120	[2]

[1] Financial information for 2015 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.

[2] Financial information for 2015 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.