Equity (Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	$ 111	[1]	$ (70)		$ (167)
Other comprehensive income (loss) before reclassifications	(53)		198		45
Amounts reclassified from AOCI	24		(6)		52
Total other comprehensive income (loss), net of tax	(29)		192	[2]	97	[2]
Less other comprehensive income attributable to noncontrolling interests			11
Accumulated other comprehensive loss, ending	(188)		111	[1]	(70)
AOCI Impact of NEP Deconsolidation	58		0	[2]	0	[2]
Cumulative Effect of New Accounting Principle in Period of Adoption	(328)
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	(77)		(100)		(170)
Other comprehensive income (loss) before reclassifications	0		0		0
Amounts reclassified from AOCI	26		32		70
Total other comprehensive income (loss), net of tax	26		32		70
Less other comprehensive income attributable to noncontrolling interests			9
Accumulated other comprehensive loss, ending	(55)		(77)		(100)
AOCI Impact of NEP Deconsolidation	3
Cumulative Effect of New Accounting Principle in Period of Adoption	(7)
Net Unrealized Gains (Losses) on Available for Sale Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	316		225		174
Other comprehensive income (loss) before reclassifications	(12)		127		69
Amounts reclassified from AOCI	1		(36)		(18)
Total other comprehensive income (loss), net of tax	(11)		91		51
Less other comprehensive income attributable to noncontrolling interests			0
Accumulated other comprehensive loss, ending	(7)		316		225
AOCI Impact of NEP Deconsolidation	0
Cumulative Effect of New Accounting Principle in Period of Adoption	(312)
Defined Benefit Pension and Other Benefits Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	(39)		(83)		(62)
Other comprehensive income (loss) before reclassifications	(14)		46		(21)
Amounts reclassified from AOCI	(3)		(2)		0
Total other comprehensive income (loss), net of tax	(17)		44		(21)
Less other comprehensive income attributable to noncontrolling interests			0
Accumulated other comprehensive loss, ending	(65)		(39)		(83)
AOCI Impact of NEP Deconsolidation	0
Cumulative Effect of New Accounting Principle in Period of Adoption	(9)
Net Unrealized Gains (Losses) on Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	(69)		(90)		(85)
Other comprehensive income (loss) before reclassifications	(31)		23		(5)
Amounts reclassified from AOCI	0		0		0
Total other comprehensive income (loss), net of tax	(31)		23		(5)
Less other comprehensive income attributable to noncontrolling interests			2
Accumulated other comprehensive loss, ending	(63)		(69)		(90)
AOCI Impact of NEP Deconsolidation	37
Cumulative Effect of New Accounting Principle in Period of Adoption	0
Other Comprehensive Income (Loss) Related to Equity Method Investee
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	(20)		(22)		(24)
Other comprehensive income (loss) before reclassifications	4		2		2
Amounts reclassified from AOCI	0		0		0
Total other comprehensive income (loss), net of tax	4		2		2
Less other comprehensive income attributable to noncontrolling interests			0
Accumulated other comprehensive loss, ending	2		$ (20)		$ (22)
AOCI Impact of NEP Deconsolidation	18
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 0

[1] Amounts have been retrospectively adjusted as discussed in Note 14.

[2] Amounts have been retrospectively adjusted as discussed in Note 14.