Investments in Unconsolidated Affiliates (Investments in Equity Method Unconsolidated Affiliates) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments In Unconsolidated Affiliates [Line Items]
Investments in unconsolidated affiliates	$ 925	$ 499
Equity in earnings (losses) of unconsolidated affiliates	(15)	69	$ 130
Electric Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in unconsolidated affiliates	93	57
Equity in earnings (losses) of unconsolidated affiliates	5	(2)	(1)
Gas Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in unconsolidated affiliates	566	113
Equity in earnings (losses) of unconsolidated affiliates	19	1	0
Commercial Renewables [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in unconsolidated affiliates	185	265
Equity in earnings (losses) of unconsolidated affiliates	(82)	(6)	8
Other [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in unconsolidated affiliates	81	64
Equity in earnings (losses) of unconsolidated affiliates	$ 43	$ 76	$ 123