Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Asset Impairment Charges	$ 282	$ 18	$ 106
Commercial Renewables [Member]
Property, Plant and Equipment [Line Items]
Asset Impairment Charges		71
Property, Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Asset Impairment Charges	58
Finite-Lived Intangible Assets [Member]
Property, Plant and Equipment [Line Items]
Asset Impairment Charges	11
Assets Leased to Others [Member] | Commercial Renewables [Member]
Property, Plant and Equipment [Line Items]
Contingent lease payments	262	$ 216	$ 172
Renewable energy projects	3,153
Accumulated depreciation and amortization	(459)
Wind Project [Member]
Property, Plant and Equipment [Line Items]
Asset Impairment Charges	$ 69