Income Taxes - Components of Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Federal:
Current	$ 100	$ 72	$ 10
Deferred	(1,040)	1,075	1,194
Total federal	(940)	1,147	1,204
State:
Current	88	76	31
Deferred	199	160	(7)
Total state	287	236	24
Total income tax expense (benefit)	(653)	1,383	1,228
FPL[Member]
Federal:
Current	168	72	423
Deferred	776	830	399
Total federal	944	902	822
State:
Current	29	57	58
Deferred	133	92	77
Total state	162	149	135
Total income tax expense (benefit)	$ 1,106	$ 1,051	$ 957