Fair Value Measurements (Reconciliation of Change in Fair Value of Derivatives, Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Realized and unrealized gains (losses):
Realized and unrealized gains (losses) reflected in operating revenues		$ 379	$ 397
Unrealized gains (losses) reflected in operating revenues, for derivatives still held at the reporting date		281	283
Derivative Financial Instruments, Net [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of net derivatives based on significant unobservable inputs at December 31 of prior year	$ 566	578	538
Realized and unrealized gains (losses):
Included in earnings	35	376	333
Included in other comprehensive income (loss)	7	(18)	8
Included in regulatory assets and liabilities	(18)	0	1
Purchases	152	126	261
Settlements	28	(317)	(390)
Issuances	(115)	(197)	(195)
Impact of adoption of new revenue standard	(30)	0	0
Transfers in	0	17	19
Transfers out	22	1	3
Fair value of net derivatives based on significant unobservable inputs at December 31	647	566	578
Gains (losses) included in earnings attributable to the change in unrealized gains (losses) relating to derivatives held at the reporting date	100	277	219
Realized and unrealized gains (losses) reflected in operating revenues	48
Unrealized gains (losses) reflected in operating revenues, for derivatives still held at the reporting date	112
FPL[Member] | Derivative Financial Instruments, Net [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of net derivatives based on significant unobservable inputs at December 31 of prior year	0	1	0
Realized and unrealized gains (losses):
Included in earnings	(1)	0	0
Included in other comprehensive income (loss)	0	0	0
Included in regulatory assets and liabilities	(18)	0	1
Purchases	(16)	0	0
Settlements	(2)	(1)	0
Issuances	0	0	0
Impact of adoption of new revenue standard	0
Transfers in	0	0	0
Transfers out	1	0	0
Fair value of net derivatives based on significant unobservable inputs at December 31	(36)	0	1
Gains (losses) included in earnings attributable to the change in unrealized gains (losses) relating to derivatives held at the reporting date	$ (1)	$ 0	$ 0