Derivative Instruments (Net Notional Volumes and Additional Disclosures) (Details) bbl in Millions, MWh in Millions, MMBTU in Millions, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) MWh MMBTU bbl	Dec. 31, 2016 USD ($) MWh MMBTU bbl
Currency Swap [Member]
Derivative [Line Items]
Notional amount | $	$ 714	$ 705
Interest Rate Contract [Member]
Derivative [Line Items]
Notional amount | $	$ 13,600	$ 15,100
Short [Member] | Commodity contract - Power [Member]
Derivative [Line Items]
Non-monetary net notional amount (in MWh) | MWh	(107)	(84)
Short [Member] | Commodity contract - Oil [Member]
Derivative [Line Items]
Non-monetary net notional amount (in barrels) | bbl	(3)	(7)
Long [Member] | Commodity contract - Natural gas [Member]
Derivative [Line Items]
Non-monetary net notional amount (in MMBtu) | MMBTU	312	1,002
FPL [Member] | Short [Member] | Commodity contract - Power [Member]
Derivative [Line Items]
Non-monetary net notional amount (in MWh) | MWh	0	0
FPL [Member] | Short [Member] | Commodity contract - Oil [Member]
Derivative [Line Items]
Non-monetary net notional amount (in barrels) | bbl	0	0
FPL [Member] | Long [Member] | Commodity contract - Natural gas [Member]
Derivative [Line Items]
Non-monetary net notional amount (in MMBtu) | MMBTU	255	618