Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	$ 982	$ 312
Special use funds [Abstract]
Equity securities	2,913	2,674
U.S. Government and municipal bonds	466	612
Corporate debt securities	764	713
Mortgage-backed securities	498	412
Other debt securities	81	52
Other Investments [Abstract]
Equity securities	35	40
Debt securities	161	171
Derivatives [Abstract]
Commodity contracts	1,938	1,937
Interest rate contracts	296	34
Foreign currency contracts	1
Derivatives [Abstract]
Commodity contracts	483	982
Interest rate contracts	292	319
Foreign currency contracts	106	127
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	982	312
Special use funds [Abstract]
Equity securities	1,410	1,320
U.S. Government and municipal bonds	296	446
Corporate debt securities	1	0
Mortgage-backed securities	0	0
Other debt securities	0	0
Other Investments [Abstract]
Equity securities	26	30
Debt securities	8	39
Derivatives [Abstract]
Commodity contracts	1,563	2,187
Interest rate contracts	0	0
Foreign currency contracts	0
Derivatives [Abstract]
Commodity contracts	1,476	2,153
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	164	61
Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	0	0
Special use funds [Abstract]
Equity securities	1,503	1,354
U.S. Government and municipal bonds	170	166
Corporate debt securities	763	713
Mortgage-backed securities	498	412
Other debt securities	81	52
Other Investments [Abstract]
Equity securities	9	10
Debt securities	153	132
Derivatives [Abstract]
Commodity contracts	1,827	2,540
Interest rate contracts	285	35
Foreign currency contracts	1
Derivatives [Abstract]
Commodity contracts	980	1,887
Interest rate contracts	171	214
Foreign currency contracts	106	132
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	1,200	1,179
Interest rate contracts	3	0
Foreign currency contracts	0
Derivatives [Abstract]
Commodity contracts	512	540
Interest rate contracts	113	101
Foreign currency contracts	0	0
FPL [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	120	36
Special use funds [Abstract]
Equity securities	1,745	1,598
U.S. Government and municipal bonds	362	480
Corporate debt securities	547	531
Mortgage-backed securities	384	327
Other debt securities	70	40
Derivatives [Abstract]
Commodity contracts	209	4
Derivatives [Abstract]
Commodity contracts	1	222
FPL [Member] | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member]
Assets [Abstract]
Cash equivalents and restricted cash - equity securities	120	36
Special use funds [Abstract]
Equity securities	373	364
U.S. Government and municipal bonds	221	335
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	120	36
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	1,372	1,234
U.S. Government and municipal bonds	141	145
Corporate debt securities	547	531
Mortgage-backed securities	384	327
Other debt securities	70	40
Derivatives [Abstract]
Commodity contracts	208	1
Derivatives [Abstract]
Commodity contracts	1	219
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	4	6
Derivatives [Abstract]
Commodity contracts	3	6
Commodity contracts [Member]
Derivatives [Abstract]
Asset offsetting	(2,652)	(3,969)
Derivatives [Abstract]
Liability offsetting	(2,485)	3,598
Commodity contracts [Member] | FPL [Member]
Derivatives [Abstract]
Asset offsetting	(3)	(3)
Derivatives [Abstract]
Liability offsetting	(3)	3
Interest Rate Contract [Member]
Derivatives [Abstract]
Asset offsetting	8	(1)
Derivatives [Abstract]
Liability offsetting	8	4
Currency Swap [Member]
Derivatives [Abstract]
Asset offsetting	0
Derivatives [Abstract]
Liability offsetting	$ 0	$ 5