Organization and Basis of Presentation (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents	$ 66	$ 92	$ 37	$ 48
Restricted cash	23	21
Accounts receivable	1,758	1,522
Property, plant, and equipment, net	20,721	19,730
Goodwill	2,293	2,286	2,018
Total Assets	33,767	32,041	$ 28,662
LIABILITIES
Current portion long-term debt, including capital leases	109	14
Mortgage bonds, notes, and other	11,039	10,506
Variable interest entity, primary beneficiary, restricted
ASSETS
Cash and cash equivalents	37	63
Restricted cash	8	7
Accounts receivable	53	42
Inventories	117	115
Property, plant, and equipment, net	475	474
Goodwill	25	17
Intangible assets	572	586
Other current and long-term assets	4	2
Total Assets	1,291	1,306
LIABILITIES
Accounts payable and accrued current liabilities	73	51
Current portion long-term debt, including capital leases	4	5
Mortgage bonds, notes, and other	1	5
Other current and long-term liabilities	17	17
Total liabilities	95	78
SGG
ASSETS
Cash and cash equivalents	23	36
Restricted cash	0	0
Accounts receivable	11	8
Inventories	3	3
Property, plant, and equipment, net	400	398
Goodwill	25	17
Intangible assets	572	586
Other current and long-term assets	4	1
Total Assets	1,038	1,049
LIABILITIES
Accounts payable and accrued current liabilities	26	19
Current portion long-term debt, including capital leases	0	0
Mortgage bonds, notes, and other	0	0
Other current and long-term liabilities	1	2
Total liabilities	$ 27	21
VIE percentage	100.00%
VIE ownership percentage	55.00%
Other
ASSETS
Cash and cash equivalents	$ 14	27
Restricted cash	8	7
Accounts receivable	42	34
Inventories	114	112
Property, plant, and equipment, net	75	76
Goodwill	0	0
Intangible assets	0	0
Other current and long-term assets	0	1
Total Assets	253	257
LIABILITIES
Accounts payable and accrued current liabilities	47	32
Current portion long-term debt, including capital leases	4	5
Mortgage bonds, notes, and other	1	5
Other current and long-term liabilities	16	15
Total liabilities	$ 68	$ 57