Organization and Basis of Presentation (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents	$ 35	$ 37	$ 99	$ 48
Restricted cash	23	23
Accounts receivable	1,185	1,276
Property, plant, and equipment, net	18,127	18,034
Total Assets	28,564	28,662
LIABILITIES
Current portion long-term debt, including capital leases	462	473
Mortgage bonds, notes, and other	8,266	8,265
Variable Interest Entity, Primary Beneficiary
ASSETS
Cash and cash equivalents	9	14
Restricted cash	7	8
Accounts receivable	14	18
Inventories	70	82
Property, plant, and equipment, net	62	66
Other current and long-term assets	3	4
Total Assets	165	192
LIABILITIES
Accounts payable and accrued current liabilities	8	13
Current portion long-term debt, including capital leases	7	8
Mortgage bonds, notes, and other	8	10
Other current and long-term liabilities	6	6
Total Liabilities	$ 29	$ 37