Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Derivatives:
Derivative assets	$ 2,140	$ 2,235
Derivatives:
Derivative liability	803	881
Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	307	982
Special use funds:
Equity securities	3,060	2,913
U.S. Government and municipal bonds	490	466
Corporate debt securities	797	764
Mortgage-backed securities	479	498
Other debt securities	115	81
Other investments:
Equity Securities	33	35
Debt securities	144	161
Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset, netting	(2,662)	(2,652)
Derivative assets	1,877	1,938
Derivatives:
Derivative liability, netting	(2,434)	(2,485)
Derivative liability	429	483
Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset, netting	4	8
Derivative assets	262	296
Derivatives:
Derivative liability, netting	4	8
Derivative liability	294	292
Fair value measurements made on a recurring basis [Member] | Foreign Currency Swap [Member]
Derivatives:
Derivative asset, netting	0	0
Derivative assets	1	1
Derivatives:
Derivative liability, netting	0	0
Derivative liability	80	106
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	307	982
Special use funds:
Equity securities	1,482	1,410
U.S. Government and municipal bonds	328	296
Corporate debt securities	1	1
Mortgage-backed securities	0	0
Other debt securities	0	0
Other investments:
Equity Securities	23	26
Debt securities	6	8
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	1,504	1,563
Derivatives:
Derivative liability before netting	1,398	1,476
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	1,578	1,503
U.S. Government and municipal bonds	162	170
Corporate debt securities	796	763
Mortgage-backed securities	479	498
Other debt securities	115	81
Other investments:
Equity Securities	10	9
Debt securities	138	153
Significant Other Observable Inputs (Level 2) [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset before netting	1,772	1,827
Derivatives:
Derivative liability before netting	1,028	980
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	254	285
Derivatives:
Derivative liability before netting	175	171
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	1	1
Derivatives:
Derivative liability before netting	80	106
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	1,263	1,200
Derivatives:
Derivative liability before netting	437	512
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements made on a recurring basis [Member] | Interest Rate Contract [Member]
Derivatives:
Derivative asset before netting	4	3
Derivatives:
Derivative liability before netting	115	113
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
FPL [Member]
Derivatives:
Derivative assets	82	209
Derivatives:
Derivative liability	5	1
FPL [Member] | Fair value measurements made on a recurring basis [Member]
Cash equivalents:
Equity securities	87	120
Special use funds:
Equity securities	1,826	1,745
U.S. Government and municipal bonds	379	362
Corporate debt securities	575	547
Mortgage-backed securities	368	384
Other debt securities	102	70
FPL [Member] | Fair value measurements made on a recurring basis [Member] | Commodity Contract [Member]
Derivatives:
Derivative asset, netting	(2)	(3)
Derivative assets	82	209
Derivatives:
Derivative liability, netting	(2)	(3)
Derivative liability	5	1
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	87	120
Special use funds:
Equity securities	386	373
U.S. Government and municipal bonds	245	221
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	1,440	1,372
U.S. Government and municipal bonds	134	141
Corporate debt securities	575	547
Mortgage-backed securities	368	384
Other debt securities	102	70
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	83	208
Derivatives:
Derivative liability before 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 before netting	1	4
Derivatives:
Derivative liability before netting	5	3
Other Current Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring [Line Items]
Restricted cash	135	164
Other Current Assets [Member] | FPL [Member]
Fair Value, Assets and Liabilities Measured on Recurring [Line Items]
Restricted cash	$ 87	$ 120