Derivative Instruments (Balance Sheet Disclosure) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative assets	$ 1,838	$ 1,804
Derivative Asset, Current	463	489
Derivative Asset, Noncurrent	1,375	1,315
Derivative liability	1,005	899
Derivative Liability, Current	483	364
Derivative Liability, Noncurrent	522	535
Current derivative assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	28	39
Non Current Derivative Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	48
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	4,263	4,012
Derivative liability, fair value, gross liability	3,354	3,107
Derivative assets	1,838	1,804
Derivative liability	1,005	899
Commodity Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	4,100	3,962
Derivative liability, fair value, gross liability	3,122	2,792
Derivative assets	1,669	1,737
Derivative liability	767	567
Interest Rate Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	163	50
Derivative liability, fair value, gross liability	203	275
Derivative assets	156	55
Derivative liability	196	280
Foreign Exchange Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	0	0
Derivative liability, fair value, gross liability	29	40
Derivative assets	13	12
Derivative liability	42	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]
Derivative Asset, Current	3	2
FPL [Member] \| Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Current	2	2
FPL [Member] \| Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Noncurrent	1
FPL [Member] \| Commodity Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	4	3
Derivative liability, fair value, gross liability	4	3
Derivative assets	3	2
Derivative liability	$ 3	$ 2

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