Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivatives:
Derivative assets	$ 2,018	$ 1,804
Derivatives:
Derivative liability	919	899
Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	227	1,294
Special use funds:
Equity securities	3,322	3,314
U.S. Government and municipal bonds	595	617
Corporate debt securities	717	765
Mortgage-backed securities	427	435
Other debt securities	141	129
Other investments:
Equity Securities	14	12
Debt securities	135	137
Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset, netting	(2,415)	(2,225)
Derivative assets	1,893	1,737
Derivatives:
Derivative liability, netting	(2,397)	(2,225)
Derivative liability	674	567
Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset, netting	1	5
Derivative assets	78	55
Derivatives:
Derivative liability, netting	(1)	(5)
Derivative liability	209	280
Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative asset, netting	12	12
Derivative assets	47	12
Derivatives:
Derivative liability, netting	(12)	(12)
Derivative liability	36	52
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	227	1,294
Special use funds:
Equity securities	1,631	1,595
U.S. Government and municipal bonds	444	478
Corporate debt securities	1	1
Mortgage-backed securities	0	0
Other debt securities	0	0
Other investments:
Equity Securities	2	2
Debt securities	32	34
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset before netting	1,030	1,303
Derivatives:
Derivative liability before netting	1,038	1,217
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset before netting	0	0
Derivatives:
Derivative liability before netting	0	0
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative asset before netting	0	0
Derivatives:
Derivative liability before netting	0	0
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	0	0
Special use funds:
Equity securities	1,691	1,719
U.S. Government and municipal bonds	151	139
Corporate debt securities	716	764
Mortgage-backed securities	427	435
Other debt securities	141	129
Other investments:
Equity Securities	12	10
Debt securities	103	103
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset before netting	2,023	1,301
Derivatives:
Derivative liability before netting	1,550	915
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset before netting	77	50
Derivatives:
Derivative liability before netting	61	143
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative asset before netting	35	0
Derivatives:
Derivative liability before netting	24	40
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	0	0
Special use funds:
Equity securities	0	0
U.S. Government and municipal bonds	0	0
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Other debt securities	0	0
Other investments:
Equity Securities	0	0
Debt securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset before netting	1,255	1,358
Derivatives:
Derivative liability before netting	483	660
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset before netting	0	0
Derivatives:
Derivative liability before netting	147	132
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative asset before netting	0	0
Derivatives:
Derivative liability before netting	0	0
Other Current Assets [Member]
Derivatives:
Restricted cash	107	159
FPL [Member]
Derivatives:
Derivative assets	2	2
Derivatives:
Derivative liability	2	2
FPL [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	117	144
Special use funds:
Equity securities	1,994	2,035
U.S. Government and municipal bonds	464	474
Corporate debt securities	545	539
Mortgage-backed securities	322	333
Other debt securities	127	116
FPL [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset, netting	(1)	(1)
Derivative assets	2	2
Derivatives:
Derivative liability, netting	(1)	(1)
Derivative liability	2	2
FPL [Member] | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	117	144
Special use funds:
Equity securities	457	473
U.S. Government and municipal bonds	346	362
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Other debt securities	0	0
FPL [Member] | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset before netting	0	0
Derivatives:
Derivative liability before netting	0	0
FPL [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	0	0
Special use funds:
Equity securities	1,537	1,562
U.S. Government and municipal bonds	118	112
Corporate debt securities	545	539
Mortgage-backed securities	322	333
Other debt securities	127	116
FPL [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset before netting	2	1
Derivatives:
Derivative liability before netting	0	1
FPL [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	0	0
Special use funds:
Equity securities	0	0
U.S. Government and municipal bonds	0	0
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Other debt securities	0	0
FPL [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset before netting	1	2
Derivatives:
Derivative liability before netting	3	2
FPL [Member] | Other Current Assets [Member]
Derivatives:
Derivative assets	2	2
Derivatives:
Restricted cash	$ 103	$ 128