Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - Fair value measurements made on a recurring basis [Member] - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Cash equivalents:
Equity securities	$ 120	$ 32
Special use funds:
Equity securities	2,829	2,634
U.S. Government and municipal bonds	628	711
Corporate debt securities	769	704
Mortgage-backed securities	363	493
Other debt securities	65	57
Other investments:
Equity Securities	39	36
Debt securities	190	175
Derivatives:
Commodity contracts	2,034	1,949
Interest rate contracts	69	50
Derivatives:
Commodity contracts	1,059	1,358
Interest rate swaps	227	266
Foreign currency swaps	141	131
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member]
Cash equivalents:
Equity securities	120	32
Special use funds:
Equity securities	1,367	1,217
U.S. Government and municipal bonds	425	520
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Other debt securities	18	25
Other investments:
Equity Securities	39	35
Debt securities	10	5
Derivatives:
Commodity contracts	1,357	1,801
Interest rate contracts	0	0
Derivatives:
Commodity contracts	1,363	1,720
Interest rate swaps	0	0
Foreign currency swaps	0	0
Significant Other Observable Inputs (Level 2) [Member]
Cash equivalents:
Equity securities	0	0
Special use funds:
Equity securities	1,462	1,417
U.S. Government and municipal bonds	203	191
Corporate debt securities	769	704
Mortgage-backed securities	363	493
Other debt securities	47	32
Other investments:
Equity Securities	0	1
Debt securities	180	170
Derivatives:
Commodity contracts	2,942	3,177
Interest rate contracts	45	35
Derivatives:
Commodity contracts	2,483	3,150
Interest rate swaps	104	126
Foreign currency swaps	141	131
Significant Unobservable Inputs (Level 3) [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
Derivatives:
Commodity contracts	1,218	1,167
Interest rate contracts	0	0
Derivatives:
Commodity contracts	575	420
Interest rate swaps	99	125
Foreign currency swaps	0	0
Netting [Member]
Derivatives:
Commodity contracts	(3,483)	(4,196)
Interest rate contracts	24	15
Derivatives:
Commodity contracts	(3,362)	(3,932)
Interest rate swaps	24	15
Foreign currency swaps	0	0
FPL [Member]
Special use funds:
Equity securities	1,720	1,561
U.S. Government and municipal bonds	498	600
Corporate debt securities	559	501
Mortgage-backed securities	293	422
Other debt securities	55	45
Derivatives:
Commodity contracts	8	7
Derivatives:
Commodity contracts	226	370
FPL [Member] | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member]
Special use funds:
Equity securities	439	324
U.S. Government and municipal bonds	336	435
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Other debt securities	18	25
Derivatives:
Commodity contracts	0	0
Derivatives:
Commodity contracts	0	0
FPL [Member] | Significant Other Observable Inputs (Level 2) [Member]
Special use funds:
Equity securities	1,281	1,237
U.S. Government and municipal bonds	162	165
Corporate debt securities	559	501
Mortgage-backed securities	293	422
Other debt securities	37	20
Derivatives:
Commodity contracts	8	2
Derivatives:
Commodity contracts	230	370
FPL [Member] | Significant Unobservable Inputs (Level 3) [Member]
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
Derivatives:
Commodity contracts	5	6
Derivatives:
Commodity contracts	1	1
FPL [Member] | Netting [Member]
Derivatives:
Commodity contracts	(5)	(1)
Derivatives:
Commodity contracts	$ (5)	$ (1)