Organization and Basis of Presentation (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
ASSETS
Cash and cash equivalents	$ 164	$ 66	$ 82
Restricted cash	22	23	$ 20
Accounts receivable	1,709	1,758
Property, plant, and equipment, net	20,870	20,721
Goodwill	2,293	2,293
Intangible assets	867	867
Total Assets	33,841	33,767
LIABILITIES
Current portion long-term debt, including capital leases	106	109
Mortgage bonds, notes, and other	11,040	11,039
Variable interest entity, primary beneficiary, restricted
ASSETS
Cash and cash equivalents	41	37
Restricted cash	8	8
Accounts receivable	48	53
Inventories	69	117
Property, plant, and equipment, net	459	475
Goodwill	25	25
Intangible assets	568	572
Other current and long-term assets	2	4
Total Assets	1,220	1,291
LIABILITIES
Accounts payable and accrued current liabilities	37	73
Current portion long-term debt, including capital leases	4	4
Mortgage bonds, notes, and other	0	1
Other current and long-term liabilities	17	17
Total liabilities	58	95
SGG
ASSETS
Cash and cash equivalents	29	23
Restricted cash	0	0
Accounts receivable	11	11
Inventories	3	3
Property, plant, and equipment, net	386	400
Goodwill	25	25
Intangible assets	568	572
Other current and long-term assets	2	4
Total Assets	1,024	1,038
LIABILITIES
Accounts payable and accrued current liabilities	2	26
Current portion long-term debt, including capital leases	0	0
Mortgage bonds, notes, and other	0	0
Other current and long-term liabilities	2	1
Total liabilities	$ 4	27
VIE ownership and non-ownership percentage	100.00%
VIE ownership percentage	55.00%
Other
ASSETS
Cash and cash equivalents	$ 12	14
Restricted cash	8	8
Accounts receivable	37	42
Inventories	66	114
Property, plant, and equipment, net	73	75
Goodwill	0	0
Intangible assets	0	0
Other current and long-term assets	0	0
Total Assets	196	253
LIABILITIES
Accounts payable and accrued current liabilities	35	47
Current portion long-term debt, including capital leases	4	4
Mortgage bonds, notes, and other	0	1
Other current and long-term liabilities	15	16
Total liabilities	$ 54	$ 68