Acquisitions, Investments and Dispositions - Pike County Light & Power Company (Details) - Pike - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Sep. 30, 2015	Aug. 31, 2016	Dec. 31, 2015
Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charge on assets held for sale			$ 5
O&R | Discontinued Operations, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business		$ 15
Period for transition services (up to)		18 months
Agreement to purchase and sell, term		3 years
Agreement to purchase and sell, term of extension option		3 years
O&R | Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charge on assets held for sale	$ 5
Impairment of long-lived assets to be disposed of, net of tax	$ 3