Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivatives:
Derivative assets	$ 1,919	$ 1,804
Derivatives:
Derivative liability	987	899
Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	259	1,294
Special use funds:
Equity securities	3,362	3,314
U.S. Government and municipal bonds	656	617
Corporate debt securities	735	765
Mortgage-backed securities	416	435
Other debt securities	140	129
Other investments:
Equity Securities	28	12
Debt securities	136	137
Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset, netting	2,305	(2,225)
Derivative assets	1,792	1,737
Derivatives:
Derivative liability, netting	2,251	(2,225)
Derivative liability	657	567
Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset, netting	1	5
Derivative assets	101	55
Derivatives:
Derivative liability, netting	1	5
Derivative liability	290	280
Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative asset, netting	(12)	12
Derivative assets	26	12
Derivatives:
Derivative liability, netting	(12)	12
Derivative liability	40	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	259	1,294
Special use funds:
Equity securities	1,610	1,595
U.S. Government and municipal bonds	502	478
Corporate debt securities	1	1
Mortgage-backed securities	0	0
Other debt securities	0	0
Other investments:
Equity Securities	16	2
Debt securities	47	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, netting	1,025	1,303
Derivatives:
Derivative liability, netting	1,008	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, netting	0	0
Derivatives:
Derivative liability, 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, netting	0	0
Derivatives:
Derivative liability, 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	1,752	1,719
U.S. Government and municipal bonds	154	139
Corporate debt securities	734	764
Mortgage-backed securities	416	435
Other debt securities	140	129
Other investments:
Equity Securities	12	10
Debt securities	89	103
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset, netting	1,772	1,301
Derivatives:
Derivative liability, netting	1,396	915
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset, netting	102	50
Derivatives:
Derivative liability, netting	145	143
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative asset, netting	14	0
Derivatives:
Derivative liability, netting	28	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, netting	1,300	1,358
Derivatives:
Derivative liability, netting	504	660
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset, netting	0	0
Derivatives:
Derivative liability, netting	146	132
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative asset, netting	0	0
Derivatives:
Derivative liability, netting	0	0
Other Current Assets [Member]
Derivatives:
Restricted cash		159
Other Current Assets [Member] | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair value measurements made on a recurring basis [Member]
Derivatives:
Restricted cash	80
FPL [Member]
Derivatives:
Derivative assets	3	2
Derivatives:
Derivative liability	3	2
FPL [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	74	144
Special use funds:
Equity securities	2,040	2,035
U.S. Government and municipal bonds	517	474
Corporate debt securities	565	539
Mortgage-backed securities	314	333
Other debt securities	123	116
FPL [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset, netting	2	(1)
Derivative assets	3	2
Derivatives:
Derivative liability, netting	2	(1)
Derivative liability	3	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	74	144
Special use funds:
Equity securities	449	473
U.S. Government and municipal bonds	396	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, netting	0	0
Derivatives:
Derivative liability, 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	1,591	1,562
U.S. Government and municipal bonds	121	112
Corporate debt securities	565	539
Mortgage-backed securities	314	333
Other debt securities	123	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, netting	2	1
Derivatives:
Derivative liability, netting	2	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, netting	3	2
Derivatives:
Derivative liability, netting	3	2
FPL [Member] | Other Current Assets [Member]
Derivatives:
Restricted cash		$ 128
FPL [Member] | Other Current Assets [Member] | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair value measurements made on a recurring basis [Member]
Derivatives:
Restricted cash	$ 61