Debt, Capitalized Interest and Other Disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Principal Payments Due on Debt
2016	$ 117
2017	950
2018	0
2019	750
2020	1,025
Thereafter	4,474
Net unamortized discount and fair value adjustments	(24)	$ (21)
Total debt	7,292	6,354
Future Minimum Rentals on Capital Lease Obligations
2016	17
2017	16
2018	16
2019	16
2020	14
Thereafter	43
Capital lease, net unamortized fair value adjustment	0
Less interest expense	(37)
Total capital lease obligations	85	32
Capitalized Interest (Textual)
Interest costs incurred, capitalized	$ 71	$ 70	$ 118