Derivatives (Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 59
Derivative Asset, Fair Value, Gross Liability		1
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		58
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 68	8
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	68	8
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	68	51
Derivative Asset, Fair Value, Gross Liability		1
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	8	50
Derivative Liability, Fair Value, Gross Liability	60
Other Current Assets [Member] \| Interest rate [Member] \| Fair Value Hedging [Member] \| Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	3
Derivative Asset, Fair Value, Gross Liability	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	3
Other Current Assets [Member] \| Commodity Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		51
Derivative Asset, Fair Value, Gross Liability		1
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		50
Other Noncurrent Assets [Member] \| Interest rate [Member] \| Fair Value Hedging [Member] \| Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1	8
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	1	$ 8
Other Noncurrent Assets [Member] \| Interest rate [Member] \| Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	64
Interest Rate Cash Flow Hedge Asset at Fair Value	64
Interest Rate Cash Flow Hedge Liability at Fair Value	0
Other Current Liabilities [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0
Derivative Asset, Fair Value, Gross Liability	60
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(60)
Other Current Liabilities [Member] \| Commodity Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0
Derivative Asset, Fair Value, Gross Liability	60
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ (60)

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value as of the balance sheet date of all interest rate derivative assets designated as cash flow hedging instruments.

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