Employee Retirement Benefits - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Target asset allocations [Abstract]
Defined contribution expense	$ 54	$ 53	$ 52
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit cost	226	241
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit cost	$ (1,284)	$ (1,427)
Weighted-average assumptions used to determine benefit obligations [Abstract]
Discount rate (in hundredths)	4.26%	3.59%
Salary increase (in hundredths)	4.40%	4.10%
Pension Benefits [Member] | Equity Securities [Member]
Target asset allocations [Abstract]
Equity investments, target allocation percentage (in hundredths)	45.00%
Pension Benefits [Member] | Debt Securities [Member]
Target asset allocations [Abstract]
Equity investments, target allocation percentage (in hundredths)	32.00%
Pension Benefits [Member] | Alternative Investments [Member]
Target asset allocations [Abstract]
Equity investments, target allocation percentage (in hundredths)	13.00%
Pension Benefits [Member] | Convertible Securities [Member]
Target asset allocations [Abstract]
Equity investments, target allocation percentage (in hundredths)	10.00%
FPL[Member]
Target asset allocations [Abstract]
Defined contribution expense	$ 34	$ 33	$ 32
FPL[Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit cost	187	208
FPL[Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit cost	$ (1,407)	$ (1,351)