Equity (Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (188)	$ 111
Other comprehensive income (loss) before reclassifications	(35)	(24)
Amounts reclassified from AOCI	11	5
Total other comprehensive loss, net of tax	(24)	(19)	[1]
Acquisition of Gulf Power	(1)
Impact of NEP deconsolidation	0	58	[1]
Adoption of accounting standards updates				$ (328)
Ending balance	(213)	(178)
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(55)	(77)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI	10	7
Total other comprehensive loss, net of tax	10	7
Acquisition of Gulf Power	(1)
Impact of NEP deconsolidation		3
Adoption of accounting standards updates				(7)
Ending balance	(46)	(74)
Net Unrealized Gains (Losses) on Available for Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(7)	316
Other comprehensive income (loss) before reclassifications	8	(5)
Amounts reclassified from AOCI	2	(1)
Total other comprehensive loss, net of tax	10	(6)
Acquisition of Gulf Power	0
Impact of NEP deconsolidation		0
Adoption of accounting standards updates				(312)
Ending balance	3	(2)
Defined Benefit Pension and Other Benefits Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(65)	(39)
Other comprehensive income (loss) before reclassifications	(52)	(1)
Amounts reclassified from AOCI	(1)	(1)
Total other comprehensive loss, net of tax	(53)	(2)
Acquisition of Gulf Power	0
Impact of NEP deconsolidation		0
Adoption of accounting standards updates				(9)
Ending balance	(118)	(50)
Net Unrealized Gains (Losses) on Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(63)	(69)
Other comprehensive income (loss) before reclassifications	10	(20)
Amounts reclassified from AOCI	0	0
Total other comprehensive loss, net of tax	10	(20)
Acquisition of Gulf Power	0
Impact of NEP deconsolidation		37
Adoption of accounting standards updates				0
Ending balance	(53)	(52)
Other Comprehensive Income (Loss) Related to Equity Method Investees
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	2	(20)
Other comprehensive income (loss) before reclassifications	(1)	2
Amounts reclassified from AOCI	0	0
Total other comprehensive loss, net of tax	(1)	2
Acquisition of Gulf Power	0
Impact of NEP deconsolidation		18
Adoption of accounting standards updates				$ 0
Ending balance	$ 1	$ 0

[1] Amounts have been retrospectively adjusted for an accounting standards update related to leases.