Debt and Interest Costs - FV, Maturities, etc. (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2017
Long-term debt
Fair value of the long-term debt	$ 7,700	$ 5,200
Carrying value	7,400	5,100
Discounts		77
Long term debt outstanding
2017	64
2018	99
2019	334
2020	3,233
2021	183
Thereafter	3,476
Letters of credit, outstanding amount	32	16
Total interest paid and accrued
Interest paid during the year (net of capitalized interest)	$ 190	$ 130	$ 169
Leverage ratio, maximum	5
Subsidiaries [Member]
Total interest paid and accrued
Equity Method Investment, Ownership Percentage	100.00%
Forecast
Total interest paid and accrued
Leverage ratio, maximum				4