Segment Information (Details) - Intersegment Reporting - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 584	$ 589	$ 2,979	$ 3,940
Operating expenses
Cost of goods sold	146	198	1,303	2,000
Operation and maintenance	204	193	662	693
Depreciation and amortization	98	93	293	281
Taxes other than income taxes	28	30	142	160
Merger-related expenses	35	0	35	0
Goodwill impairment	14	0	14	0
Total operating expenses	525	514	2,449	3,134
Gain on disposition of assets	0	3	0	3
Operating income	59	78	530	809
Other income	2	3	9	8
EBIT	61	81	539	817
Total assets	14,206	13,932	14,206	13,932	$ 14,888
Capital expenditures	293	211	745	543
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(41)	(41)	(160)	(216)
Operating expenses
Cost of goods sold	(40)	(39)	(156)	(210)
Operation and maintenance	(1)	(2)	(4)	(6)
Depreciation and amortization	0	0	0	0
Taxes other than income taxes	0	0	0	0
Merger-related expenses	0		0
Goodwill impairment	0		0
Total operating expenses	(41)	(41)	(160)	(216)
Gain on disposition of assets		0		0
Operating income	0	0	0	0
Other income	0	0	0	0
EBIT	0	0	0	0
Total assets	(9,435)	(9,253)	(9,435)	(9,253)	(9,621)
Capital expenditures	0	0	0	0
Distribution Operations [Member]
Operating expenses
Goodwill impairment			0
Distribution Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	445	474	2,332	2,974
Operating expenses
Cost of goods sold	96	138	1,038	1,655
Operation and maintenance	158	145	503	515
Depreciation and amortization	83	79	248	235
Taxes other than income taxes	23	24	128	146
Merger-related expenses	0		0
Goodwill impairment	0		0
Total operating expenses	360	386	1,917	2,551
Gain on disposition of assets		0		0
Operating income	85	88	415	423
Other income	1	1	5	5
EBIT	86	89	420	428
Total assets	12,096	11,624	12,096	11,624	12,037
Capital expenditures	273	196	691	504
Retail Operations [Member]
Operating expenses
Goodwill impairment			0
Retail Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	134	146	628	729
Operating expenses
Cost of goods sold	86	99	391	498
Operation and maintenance	29	34	100	105
Depreciation and amortization	7	7	19	21
Taxes other than income taxes	1	1	3	3
Merger-related expenses	0		0
Goodwill impairment	0		0
Total operating expenses	123	141	513	627
Gain on disposition of assets		0		0
Operating income	11	5	115	102
Other income	0	0	0	0
EBIT	11	5	115	102
Total assets	645	663	645	663	670
Capital expenditures	2	3	6	9
Wholesale Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	34	5	128	383
Operating expenses
Cost of goods sold	1	3	10	13
Operation and maintenance	14	10	49	59
Depreciation and amortization	0	0	1	1
Taxes other than income taxes	1	1	2	2
Merger-related expenses	0		0
Goodwill impairment	0		0
Total operating expenses	16	14	62	75
Gain on disposition of assets		3		3
Operating income	18	(6)	66	311
Other income	0	(1)	0	(3)
EBIT	18	(7)	66	308
Total assets	913	1,056	913	1,056	1,402
Capital expenditures	1	0	2	1
Midstream Operations [Member]
Operating expenses
Goodwill impairment			14
Midstream Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	12	4	42	65
Operating expenses
Cost of goods sold	3	(3)	15	44
Operation and maintenance	6	5	18	18
Depreciation and amortization	4	5	13	14
Taxes other than income taxes	1	1	3	4
Merger-related expenses	0		0
Goodwill impairment	14		14
Total operating expenses	28	8	63	80
Gain on disposition of assets		0		0
Operating income	(16)	(4)	(21)	(15)
Other income	0	0	1	1
EBIT	(16)	(4)	(20)	(14)
Total assets	680	692	680	692	694
Capital expenditures	8	3	18	8
Other Segments [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	1	9	5
Operating expenses
Cost of goods sold	0	0	5	0
Operation and maintenance	(2)	1	(4)	2
Depreciation and amortization	4	2	12	10
Taxes other than income taxes	2	3	6	5
Merger-related expenses	35		35
Goodwill impairment	0		0
Total operating expenses	39	6	54	17
Gain on disposition of assets		0		0
Operating income	(39)	(5)	(45)	(12)
Other income	1	3	3	5
EBIT	(38)	(2)	(42)	(7)
Total assets	9,307	9,150	9,307	9,150	$ 9,706
Capital expenditures	9	9	28	21
Reportable Subsegments [Member]
Segment Reporting Information [Line Items]
Operating revenues	584	589	2,979	3,940
Reportable Subsegments [Member] | Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(6)	(6)	(29)	(62)
Reportable Subsegments [Member] | Distribution Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	410	439	2,201	2,821
Reportable Subsegments [Member] | Retail Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	134	146	628	728
Reportable Subsegments [Member] | Wholesale Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	34	5	128	383
Reportable Subsegments [Member] | Midstream Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	12	4	42	65
Reportable Subsegments [Member] | Other Segments [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	1	9	5
Intercompany revenues [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Intercompany revenues [Member] | Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(35)	(35)	(131)	(154)
Intercompany revenues [Member] | Distribution Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	35	35	131	153
Intercompany revenues [Member] | Retail Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	1
Intercompany revenues [Member] | Wholesale Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Intercompany revenues [Member] | Midstream Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Intercompany revenues [Member] | Other Segments [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 0	$ 0	$ 0	$ 0