Organization and Basis of Presentation (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	$ 63	$ 66
Restricted cash	23	23
Accounts receivable	1,690	1,758
Property, plant, and equipment, net	21,239	20,721
Goodwill	2,293	2,293
Intangible assets	862	867
Total Assets	34,330	33,767
LIABILITIES
Current portion long-term debt, including capital leases	5	109
Mortgage bonds, notes, and other	11,560	11,039
Variable interest entity, primary beneficiary, restricted
ASSETS
Cash and cash equivalents	44	37
Restricted cash	8	8
Accounts receivable	42	53
Inventories	70	117
Property, plant, and equipment, net	457	475
Goodwill	25	25
Intangible assets	564	572
Other current and long-term assets	3	4
Total Assets	1,213	1,291
LIABILITIES
Accounts payable and accrued current liabilities	37	73
Current portion long-term debt, including capital leases	3	4
Mortgage bonds, notes, and other	0	1
Other current and long-term liabilities	22	17
Total liabilities	62	95
SGG
ASSETS
Cash and cash equivalents	28	23
Restricted cash	0	0
Accounts receivable	10	11
Inventories	3	3
Property, plant, and equipment, net	389	400
Goodwill	25	25
Intangible assets	564	572
Other current and long-term assets	2	4
Total Assets	1,021	1,038
LIABILITIES
Accounts payable and accrued current liabilities	5	26
Current portion long-term debt, including capital leases	0	0
Mortgage bonds, notes, and other	0	0
Other current and long-term liabilities	7	1
Total liabilities	$ 12	27
VIE ownership and non-ownership percentage	100.00%
VIE ownership percentage	55.00%
Other
ASSETS
Cash and cash equivalents	$ 16	14
Restricted cash	8	8
Accounts receivable	32	42
Inventories	67	114
Property, plant, and equipment, net	68	75
Goodwill	0	0
Intangible assets	0	0
Other current and long-term assets	1	0
Total Assets	192	253
LIABILITIES
Accounts payable and accrued current liabilities	32	47
Current portion long-term debt, including capital leases	3	4
Mortgage bonds, notes, and other	0	1
Other current and long-term liabilities	15	16
Total liabilities	$ 50	$ 68