Derivative Instruments (Balance Sheet Disclosure) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative assets	$ 1,919	$ 1,804
Derivative Asset, Current	459	489
Derivative Asset, Noncurrent	1,460	1,315
Derivative liability	987	899
Derivative Liability, Current	496	364
Derivative Liability, Noncurrent	491	535
Current derivative assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	11	39
Non Current Derivative Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	43
Noncurrent derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, collateral, right to reclaim cash, offset		39
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	4,213	4,012
Derivative liability, fair value, gross liability	3,227	3,107
Derivative assets	1,919	1,804
Derivative liability	987	899
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	4,097	3,962
Derivative liability, fair value, gross liability	2,908	2,792
Derivative assets	1,792	1,737
Derivative liability	657	567
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	102	50
Derivative liability, fair value, gross liability	291	275
Derivative assets	101	55
Derivative liability	290	280
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	14	0
Derivative liability, fair value, gross liability	28	40
Derivative assets	26	12
Derivative liability	40	52
FPL [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	3	2
Derivative liability	3	2
FPL [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Current Assets Derviatives	3	2
FPL [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability	2	2
FPL [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability	1
FPL [Member] | Commodity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	5	3
Derivative liability, fair value, gross liability	5	3
Derivative assets	3	2
Derivative liability	$ 3	$ 2