Fair Value Measurements (Reconciliation of Changes in the Fair Value) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair value based on significant unobservable inputs, beginning balance	$ 564	$ 578
Realized and unrealized gains (losses): [Abstract]
Included in Earnings	16	216
Included in other comprehensive income	(3)	(1)
Included in regulatory assets and liabilities	(1)	(2)
Purchases	42	21
Settlements	48	(85)
Issuances	(33)	(16)
Impact of adoption of new revenue standard	(30)	0
Transfers in	0	9
Transfers out	22	(5)
Fair value based on significant unobservable inputs, ending balance	625	715
The amount of gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to derivatives still held at the reporting date	19	141
Realized and unrealized gains (losses) reflected in operating revenues	26	215
Unrealized gains (losses) reflected in operating revenues related to derivatives still held at the reporting date	29	141
FPL [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair value based on significant unobservable inputs, beginning balance	0	1
Realized and unrealized gains (losses): [Abstract]
Included in Earnings	0	0
Included in other comprehensive income	0	0
Included in regulatory assets and liabilities	(2)	(2)
Purchases	0	0
Settlements	0	(3)
Issuances	0	0
Impact of adoption of new revenue standard	0	0
Transfers in	0	0
Transfers out	0	0
Fair value based on significant unobservable inputs, ending balance	(2)	(4)
The amount of gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to derivatives still held at the reporting date	$ 0	$ 0