Organization and Basis of Presentation (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	$ 84	$ 66
Restricted cash	20	23
Accounts receivable	1,690	1,758
Property, plant, and equipment, net	21,612	20,721
Goodwill	2,293	2,293
Intangible assets	864	867
Total Assets	35,292	33,767
LIABILITIES
Current portion long-term debt, including capital leases	1	109
Mortgage bonds, notes, and other	12,475	11,039
Variable interest entity, primary beneficiary, restricted
ASSETS
Cash and cash equivalents	38	37
Restricted cash	4	8
Accounts receivable	41	53
Inventories	65	117
Property, plant, and equipment, net	442	475
Goodwill	25	25
Intangible assets	561	572
Other current and long-term assets	1	4
Total Assets	1,177	1,291
LIABILITIES
Accounts payable and accrued current liabilities	32	73
Current portion long-term debt, including capital leases	0	4
Mortgage bonds, notes, and other	0	1
Other current and long-term liabilities	13	17
Total liabilities	45	95
SGG
ASSETS
Cash and cash equivalents	23	23
Restricted cash	0	0
Accounts receivable	9	11
Inventories	3	3
Property, plant, and equipment, net	392	400
Goodwill	25	25
Intangible assets	561	572
Other current and long-term assets	1	4
Total Assets	1,014	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	7	1
Total liabilities	$ 9	27
VIE ownership and non-ownership percentage	100.00%
VIE ownership percentage	55.00%
Other
ASSETS
Cash and cash equivalents	$ 15	14
Restricted cash	4	8
Accounts receivable	32	42
Inventories	62	114
Property, plant, and equipment, net	50	75
Goodwill	0	0
Intangible assets	0	0
Other current and long-term assets	0	0
Total Assets	163	253
LIABILITIES
Accounts payable and accrued current liabilities	30	47
Current portion long-term debt, including capital leases	0	4
Mortgage bonds, notes, and other	0	1
Other current and long-term liabilities	6	16
Total liabilities	$ 36	$ 68