Non-wholly Owned Entities - SouthStars Revenues and Expenses (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Variable Interest Entity [Line Items]
Operating revenues	$ 962	$ 584	$ 674	$ 1,721	$ 1,445	$ 589	$ 889	$ 2,462	$ 3,941	$ 5,385	$ 4,209
Operating expenses
Cost of goods sold									1,645	2,765	2,110
Operation and maintenance									914	939	887
Depreciation and amortization									397	380	397
Taxes other than income taxes									181	208	187
Total operating expenses									3,195	4,292	3,581
Operating income	$ 216	$ 59	$ 107	$ 364	$ 286	$ 78	$ 139	$ 592	746	1,095	$ 639
South Star [Member]
Variable Interest Entity [Line Items]
Operating revenues									711	866
Operating expenses
Cost of goods sold									490	645
Operation and maintenance									81	87
Depreciation and amortization									10	11
Taxes other than income taxes									1	1
Total operating expenses									582	744
Operating income									$ 129	$ 122