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Acquisitions and Dispositions Acquisitions and Dispositions (Purchase Price Allocation) (Details) - USD ($) $ in Millions	Oct. 03, 2016	Sep. 30, 2016	Dec. 31, 2015
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]
Goodwill		$ 16,354	$ 16,343
Piedmont Natural Gas [Member] \| Piedmont Acquisition
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]
Current assets	$ 500
Property, plant and equipment, net	4,710
Goodwill	3,380
Other long-term assets	810
Total assets	9,400
Current liabilities, including current maturities of long-term debt	590
Long-term liabilities	1,810
Long-term debt	2,000
Total liabilities	4,400
Total purchase price	$ 5,000