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, 2018 USD ($) MWh MMBTU bbl	Dec. 31, 2017 USD ($) MWh MMBTU bbl
Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount | $	$ 15,900	$ 12,100
Currency Swap [Member]
Derivative [Line Items]
Notional amount | $	$ 656	$ 718
Short [Member] | Commodity contract - Power [Member]
Derivative [Line Items]
Non-monetary net notional amount (in MWh) | MWh	(108)	(109)
Short [Member] | Commodity contract - Natural gas [Member]
Derivative [Line Items]
Non-monetary net notional amount (in MMBtu) | MMBTU	257	74
Short [Member] | Commodity contract - Oil [Member]
Derivative [Line Items]
Non-monetary net notional amount (in barrels) | bbl	(28)	(15)
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	307	142