Employee Retirement Benefits - Plan Assets, Benefit Obligations and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in pension plan assets:
Plan assets, beginning balance	$ 3,563
Plan assets, ending balance	3,651	$ 3,563
Pension Benefits [Member]
Change in pension plan assets:
Plan assets, beginning balance	3,563	3,698
Actual return on plan assets	217	(8)
Benefit payments	(129)	(127)
Plan assets, ending balance	3,651	3,563	$ 3,698
Change in pension benefit obligation:
Obligation, beginning balance	2,408	2,454
Service cost	62	70	61
Interest cost	105	97	101
Plan amendments	(19)	0
Actuarial losses (gains) - net	47	(86)
Benefit payments	(129)	(127)
Obligation, ending balance	2,474	2,408	$ 2,454
Funded status:
Prepaid (accrued) benefit cost	1,177	1,155
Accumulated benefit obligation	2,439	2,366
Pension Benefits [Member] | FPL [Member]
Funded status:
Prepaid (accrued) benefit cost	$ 1,301	$ 1,243