Fair Value Measurements (Reconciliation of Changes in the Fair Value) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair value based on significant unobservable inputs, beginning balance	$ 715	$ 649	$ 578	$ 538
Realized and unrealized gains (losses): [Abstract]
Included in Earnings	144	(34)	360	220
Included in other comprehensive income	(10)	3	(11)	(3)
Included in regulatory assets and liabilities	0	3	(2)	0
Purchases	23	75	45	175
Settlements	(72)	(95)	(157)	(228)
Issuances	(88)	(69)	(104)	(143)
Transfers in	6	0	14	3
Transfers out	6	0	1	(30)
Fair value based on significant unobservable inputs, ending balance	724	532	724	532
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	135	(38)	284	125
Realized and unrealized gains (losses) reflected in operating revenues	140	(28)	356	246
Unrealized gains (losses) reflected in operating revenues related to derivatives still held at the reporting date	131	(32)	280	151
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	(4)	(8)	1	0
Realized and unrealized gains (losses): [Abstract]
Included in Earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Included in regulatory assets and liabilities	0	3	(2)	0
Purchases	0	0	0	0
Settlements	2	4	(1)	(1)
Issuances	0	0	0	0
Transfers in	0	0	0	0
Transfers out	0	0	0	0
Fair value based on significant unobservable inputs, ending balance	(2)	(1)	(2)	(1)
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	$ 0	$ 0