Fair Value Measurements (Gains and Losses on Available-for-sale Debt Securities) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Securities [Member]
Marketable Securities, Available-for-sale [Line Items]
Realized Gains	$ 21	$ 5	$ 47	$ 32
Realized Losses	14	9	34	49
Proceeds from sale or maturity of securities	612	576	2,087	1,889
Available for sale securities: Special Use Funds - Debt Securities [Member]
Marketable Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	88		88		$ 14
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	9		9		52
Fair value of available for sale securities in an unrealized loss position	264		264		1,273
FPL [Member] \| Debt Securities [Member]
Marketable Securities, Available-for-sale [Line Items]
Realized Gains	15	2	30	22
Realized Losses	11	5	20	34
Proceeds from sale or maturity of securities	489	$ 487	1,717	$ 1,529
FPL [Member] \| Available for sale securities: Special Use Funds - Debt Securities [Member]
Marketable Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	68		68		11
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	8		8		41
Fair value of available for sale securities in an unrealized loss position	$ 191		$ 191		$ 961

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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