Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Net cash provided by (used in) operating activities included:
Interest paid (net of amounts capitalized)	$ (87)	$ (55)
Income taxes paid to taxing authorities	(15)	(47)
Noncash investing activities:
Asset retirement costs capitalized	2	21
Asset retirement obligations assumed by buyer	$ 54	$ 0