Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	$ 1,294	$ 982
Special use funds [Abstract]
Equity securities	3,314	2,913
U.S. Government and municipal bonds	617	466
Corporate debt securities	765	764
Mortgage-backed securities	435	498
Other debt securities	129	81
Other Investments [Abstract]
Equity securities	12	35
Debt securities	137	161
Derivatives [Abstract]
Commodity contracts	1,737	1,938
Interest rate contracts	55	296
Foreign currency contracts	12	1
Derivatives [Abstract]
Commodity contracts	567	483
Interest rate contracts	280	292
Foreign currency contracts	52	106
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	1,294	982
Special use funds [Abstract]
Equity securities	1,595	1,410
U.S. Government and municipal bonds	478	296
Corporate debt securities	1	1
Mortgage-backed securities	0	0
Other debt securities	0	0
Other Investments [Abstract]
Equity securities	2	26
Debt securities	34	8
Derivatives [Abstract]
Commodity contracts	1,303	1,563
Interest rate contracts	0	0
Foreign currency contracts	0	0
Derivatives [Abstract]
Commodity contracts	1,217	1,476
Interest rate contracts	0	0
Foreign currency contracts	0	0
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Current other assets [Member]
Assets [Abstract]
Restricted cash	159	164
Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	0	0
Special use funds [Abstract]
Equity securities	1,719	1,503
U.S. Government and municipal bonds	139	170
Corporate debt securities	764	763
Mortgage-backed securities	435	498
Other debt securities	129	81
Other Investments [Abstract]
Equity securities	10	9
Debt securities	103	153
Derivatives [Abstract]
Commodity contracts	1,301	1,827
Interest rate contracts	50	285
Foreign currency contracts	0	1
Derivatives [Abstract]
Commodity contracts	915	980
Interest rate contracts	143	171
Foreign currency contracts	40	106
Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	0	0
Special use funds [Abstract]
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 [Abstract]
Equity securities	0	0
Debt securities	0	0
Derivatives [Abstract]
Commodity contracts	1,358	1,200
Interest rate contracts	0	3
Foreign currency contracts	0	0
Derivatives [Abstract]
Commodity contracts	660	512
Interest rate contracts	132	113
Foreign currency contracts	0	0
Commodity contracts [Member]
Derivatives [Abstract]
Asset offsetting	(2,225)	(2,652)
Derivatives [Abstract]
Liability offsetting	(2,225)	2,485
Interest Rate Contract [Member]
Derivatives [Abstract]
Asset offsetting	5	8
Derivatives [Abstract]
Liability offsetting	5	8
Currency Swap [Member]
Derivatives [Abstract]
Asset offsetting	(12)	0
Derivatives [Abstract]
Liability offsetting	12
FPL[Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	144	120
Special use funds [Abstract]
Equity securities	2,035	1,745
U.S. Government and municipal bonds	474	362
Corporate debt securities	539	547
Mortgage-backed securities	333	384
Other debt securities	116	70
Derivatives [Abstract]
Commodity contracts	2	209
Derivatives [Abstract]
Commodity contracts	2	1
FPL[Member] | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	144	120
Special use funds [Abstract]
Equity securities	473	373
U.S. Government and municipal bonds	362	221
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Other debt securities	0	0
Derivatives [Abstract]
Commodity contracts	0	0
Derivatives [Abstract]
Commodity contracts	0	0
FPL[Member] | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Current other assets [Member]
Assets [Abstract]
Restricted cash	128	120
FPL[Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	0	0
Special use funds [Abstract]
Equity securities	1,562	1,372
U.S. Government and municipal bonds	112	141
Corporate debt securities	539	547
Mortgage-backed securities	333	384
Other debt securities	116	70
Derivatives [Abstract]
Commodity contracts	1	208
Derivatives [Abstract]
Commodity contracts	1	1
FPL[Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	0	0
Special use funds [Abstract]
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 [Abstract]
Commodity contracts	2	4
Derivatives [Abstract]
Commodity contracts	2	3
FPL[Member] | Commodity contracts [Member]
Derivatives [Abstract]
Asset offsetting	(1)	(3)
Derivatives [Abstract]
Liability offsetting	$ (1)	$ 3