Employee Retirement Benefits - Net Periodic Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets, Net of Management Fees	7.35%	7.35%
Net periodic benefit (income) cost [Abstract]
Service cost	$ 66	$ 62	$ 70
Interest cost	83	105	97
Expected return on plan assets	(270)	(260)	(253)
Amortization of prior service cost (benefit)	(1)	1	1
Amortization of losses	0	0	0
Special termination benefits	38	0	0
Postretirement benefits settlement	0	0	0
Net periodic (income) cost	(84)	(92)	(85)
Other Benefits [Member]
Net periodic benefit (income) cost [Abstract]
Service cost	1	2	3
Interest cost	8	13	13
Expected return on plan assets	0	(1)	(1)
Amortization of prior service cost (benefit)	(10)	(2)	(3)
Amortization of losses	0	0	2
Special termination benefits	0	0	0
Postretirement benefits settlement	1	0	0
Net periodic (income) cost	0	12	14
FPL[Member] | Pension Benefits [Member]
Net periodic benefit (income) cost [Abstract]
Net periodic (income) cost	(51)	(58)	(55)
FPL[Member] | Other Benefits [Member]
Net periodic benefit (income) cost [Abstract]
Net periodic (income) cost	$ 0	$ 9	$ 11