Investments in Unconsolidated Affiliates (Investments in Equity Method Unconsolidated Affiliates) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	$ 1,175	$ 925
Equity in earnings (losses) of unconsolidated affiliates	119	(15)	$ 69
Electric Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	89	93
Equity in earnings (losses) of unconsolidated affiliates	5	5	(2)
Gas Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	763	566
Equity in earnings (losses) of unconsolidated affiliates	62	19	1
Commercial Renewables [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	190	185
Equity in earnings (losses) of unconsolidated affiliates	(5)	(82)	(6)
Other [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	133	81
Equity in earnings (losses) of unconsolidated affiliates	$ 57	$ 43	$ 76