Business Acquisitions and Dispositions Business Acquisitions and Dispositions - Dominion (Details 4) $ in Millions	Mar. 31, 2014 USD ($) customer	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 662	$ 999
Business Acquisition, Goodwill, Expected Tax Deductible Amount		$ 547	$ 620
Dominion [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 192
Business Acquisitions, Consideration Transferred, Purchase Price	165
Business Acquisition, Consideration Transferred, Working Capital	27
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	40
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other	14
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Derivative Assets	21
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	47
Goodwill	91
Business Acquisition, Goodwill, Expected Tax Deductible Amount	$ 8
Scenario, Plan [Member] | Dominion [Member]
Business Acquisition [Line Items]
Business Acquisition, Customers Acquired | customer	540,000
Customer Relationships [Member] | Dominion [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	$ 64
Trade Names [Member] | Dominion [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	$ 9