Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivatives:
Derivative assets	$ 1,838	$ 1,804
Derivatives:
Derivative liability	1,005	899
Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	255	1,294
Special use funds:
Equity securities	3,560	3,314
U.S. Government and municipal bonds	634	617
Corporate debt securities	726	765
Mortgage-backed securities	428	435
Other debt securities	146	129
Other investments:
Equity Securities	28	12
Debt securities	131	137
Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset, netting	(2,431)	(2,225)
Derivative assets	1,669	1,737
Derivatives:
Derivative liability, netting	(2,355)	(2,225)
Derivative liability	767	567
Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset, netting	(7)	5
Derivative assets	156	55
Derivatives:
Derivative liability, netting	(7)	5
Derivative liability	196	280
Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative asset, netting	13	12
Derivative assets	13	12
Derivatives:
Derivative liability, netting	13	12
Derivative liability	42	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	255	1,294
Special use funds:
Equity securities	1,687	1,595
U.S. Government and municipal bonds	479	478
Corporate debt securities	1	1
Mortgage-backed securities	0	0
Other debt securities	0	0
Other investments:
Equity Securities	16	2
Debt securities	44	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, Gross Asset	1,256	1,303
Derivatives:
Derivative Liability, Gross Liability	1,224	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, Gross Asset	0	0
Derivatives:
Derivative Liability, Gross Liability	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, Gross Asset	0	0
Derivatives:
Derivative Liability, Gross Liability	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	1,873	1,719
U.S. Government and municipal bonds	155	139
Corporate debt securities	725	764
Mortgage-backed securities	428	435
Other debt securities	146	129
Other investments:
Equity Securities	12	10
Debt securities	87	103
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative Asset, Gross Asset	1,617	1,301
Derivatives:
Derivative Liability, Gross Liability	1,341	915
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative Asset, Gross Asset	163	50
Derivatives:
Derivative Liability, Gross Liability	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, Gross Asset	0	0
Derivatives:
Derivative Liability, Gross Liability	29	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, Gross Asset	1,227	1,358
Derivatives:
Derivative Liability, Gross Liability	557	660
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative Asset, Gross Asset	0	0
Derivatives:
Derivative Liability, Gross Liability	142	132
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative Asset, Gross Asset	0	0
Derivatives:
Derivative Liability, Gross Liability	0	0
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	79	159
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	167	144
Special use funds:
Equity securities	2,179	2,035
U.S. Government and municipal bonds	500	474
Corporate debt securities	548	539
Mortgage-backed securities	319	333
Other debt securities	130	116
FPL [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset, netting	(1)	(1)
Derivative assets	3	2
Derivatives:
Derivative liability, netting	(1)	(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	167	144
Special use funds:
Equity securities	478	473
U.S. Government and municipal bonds	380	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, Gross Asset	0	0
Derivatives:
Derivative Liability, Gross Liability	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	1,701	1,562
U.S. Government and municipal bonds	120	112
Corporate debt securities	548	539
Mortgage-backed securities	319	333
Other debt securities	130	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, Gross Asset	2	1
Derivatives:
Derivative Liability, Gross Liability	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, Gross Asset	2	2
Derivatives:
Derivative Liability, Gross Liability	4	2
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	$ 76	$ 128