Employee Retirement Benefits - Plan Assets, Benefit Obligations and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in pension plan assets:
Plan assets, beginning balance	$ 3,651
Plan assets, ending balance	4,020	$ 3,651
Pension Benefits [Member]
Change in pension plan assets:
Plan assets, beginning balance	3,651	3,563
Actual return on plan assets	574	217
Benefit payments	205	129
Plan assets, ending balance	4,020	3,651	$ 3,563
Change in pension benefit obligation:
Obligation, beginning balance	2,474	2,408
Service cost	66	62	70
Interest cost	83	105	97
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits	38	0
Plan amendments	12	(19)
Actuarial losses - net	125	47
Benefit payments	205	129
Obligation, ending balance	2,593	2,474	$ 2,408
Funded status:
Prepaid (accrued) benefit cost	1,427	1,177
Accumulated benefit obligation	2,548	2,439
FPL[Member] | Pension Benefits [Member]
Funded status:
Prepaid (accrued) benefit cost	$ 1,351	$ 1,301