Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	$ 234,000,000	$ 32,000,000
Special use funds:
Equity securities	2,531,000,000	2,634,000,000
U.S. Government and municipal bonds	629,000,000	711,000,000
Corporate debt securities	775,000,000	704,000,000
Mortgage-backed securities	369,000,000	493,000,000
Other debt securities	61,000,000	57,000,000
Other investments:
Equity Securities	38,000,000	36,000,000
Debt securities	184,000,000	175,000,000
Derivatives:
Commodity contracts	1,903,000,000	1,949,000,000
Interest rate contracts	55,000,000	50,000,000
Derivatives:
Commodity contracts	866,000,000	1,358,000,000
Interest rate swaps	340,000,000	266,000,000
Foreign currency swaps	137,000,000	131,000,000
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	234,000,000	32,000,000
Special use funds:
Equity securities	1,185,000,000	1,217,000,000
U.S. Government and municipal bonds	425,000,000	520,000,000
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Other debt securities	18,000,000	25,000,000
Other investments:
Equity Securities	38,000,000	35,000,000
Debt securities	15,000,000	5,000,000
Derivatives:
Commodity contracts	1,446,000,000	1,801,000,000
Interest rate contracts	0	0
Derivatives:
Commodity contracts	1,421,000,000	1,720,000,000
Interest rate swaps	0	0
Foreign currency swaps	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	1,346,000,000	1,417,000,000
U.S. Government and municipal bonds	204,000,000	191,000,000
Corporate debt securities	775,000,000	704,000,000
Mortgage-backed securities	369,000,000	493,000,000
Other debt securities	43,000,000	32,000,000
Other investments:
Equity Securities	0	1,000,000
Debt securities	169,000,000	170,000,000
Derivatives:
Commodity contracts	3,094,000,000	3,177,000,000
Interest rate contracts	53,000,000	35,000,000
Derivatives:
Commodity contracts	2,418,000,000	3,150,000,000
Interest rate swaps	223,000,000	126,000,000
Foreign currency swaps	137,000,000	131,000,000
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
Derivatives:
Commodity contracts	1,170,000,000	1,167,000,000
Interest rate contracts	0	0
Derivatives:
Commodity contracts	509,000,000	420,000,000
Interest rate swaps	115,000,000	125,000,000
Foreign currency swaps	0	0
Netting [Member] | Fair value measurements made on a recurring basis [Member]
Derivatives:
Commodity contracts	(3,807,000,000)	(4,196,000,000)
Interest rate contracts	2,000,000	15,000,000
Derivatives:
Commodity contracts	(3,482,000,000)	(3,932,000,000)
Interest rate swaps	2,000,000	15,000,000
Foreign currency swaps	0	0
FPL [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	48,000,000
Special use funds:
Equity securities	1,508,000,000	1,561,000,000
U.S. Government and municipal bonds	503,000,000	600,000,000
Corporate debt securities	562,000,000	501,000,000
Mortgage-backed securities	295,000,000	422,000,000
Other debt securities	53,000,000	45,000,000
Derivatives:
Commodity contracts	5,000,000	7,000,000
Derivatives:
Commodity contracts	235,000,000	370,000,000
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	48,000,000
Special use funds:
Equity securities	332,000,000	324,000,000
U.S. Government and municipal bonds	333,000,000	435,000,000
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Other debt securities	17,000,000	25,000,000
Derivatives:
Commodity contracts	0	0
Derivatives:
Commodity contracts	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
Special use funds:
Equity securities	1,176,000,000	1,237,000,000
U.S. Government and municipal bonds	170,000,000	165,000,000
Corporate debt securities	562,000,000	501,000,000
Mortgage-backed securities	295,000,000	422,000,000
Other debt securities	36,000,000	20,000,000
Derivatives:
Commodity contracts	1,000,000	2,000,000
Derivatives:
Commodity contracts	233,000,000	370,000,000
FPL [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	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
Derivatives:
Commodity contracts	5,000,000	6,000,000
Derivatives:
Commodity contracts	3,000,000	1,000,000
FPL [Member] | Netting [Member] | Fair value measurements made on a recurring basis [Member]
Derivatives:
Commodity contracts	(1,000,000)	(1,000,000)
Derivatives:
Commodity contracts	(1,000,000)	$ (1,000,000)
Other Current Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring [Line Items]
Restricted cash	60,000,000
Other Current Assets [Member] | FPL [Member]
Fair Value, Assets and Liabilities Measured on Recurring [Line Items]
Restricted cash	48,000,000
Other Noncurrent Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring [Line Items]
Restricted cash	3,000,000
Other Noncurrent Assets [Member] | FPL [Member]
Fair Value, Assets and Liabilities Measured on Recurring [Line Items]
Restricted cash	$ 0