Derivative and Hedging Activities - Narrative (Details) € in Millions, MMBoe in Millions, $ in Millions, MMBTU in Billions	1 Months Ended		3 Months Ended
	Dec. 31, 2015 USD ($) Derivatives $ / €	Dec. 31, 2006 USD ($) $ / €	Mar. 31, 2016 USD ($) MMBoe MMBTU counterparty Derivatives $ / €	Mar. 31, 2016 EUR (€) MMBoe counterparty Derivatives $ / €	Dec. 31, 2015 EUR (€) Derivatives $ / €	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2006 EUR (€) $ / €
Derivative [Line Items]
Number of Interest Rate Derivatives Held | Derivatives	0		0	0	0
Gain (Loss) on Repurchase of Debt Instrument			$ 100
Derivative Assets (Liabilities), at Fair Value, Net	$ 512		515			$ 512
Debt Instrument, Face Amount	9,706		9,425
Accumulated other comprehensive loss	99		99
Expected amount to be transferred of during the next 12 months			$ 21
6.25% Euro-Denominated Senior Notes Due 2017 [ Member] | Senior Notes [Member]
Derivative [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.25%	6.25%
Debt Instrument, Face Amount	329		$ 344
Cash Flow Hedging [Member]
Derivative [Line Items]
Accumulated other comprehensive loss	99		99			134	$ 143
Cash Flow Hedging [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Derivative [Line Items]
Accumulated other comprehensive loss			$ 109
Interest Rate Contract [Member]
Derivative [Line Items]
Amortization Period of Deferred Gain (Loss) on Discontinuation of Fair Value Hedge			6 years
Deferred (Gain) Loss on Discontinuation of Fair Value Hedge			$ 7
Debt Instrument, Face Amount	$ 0		$ 0
Cross Currency Interest Rate Contract [Member] | 6.25% Euro-Denominated Senior Notes Due 2017 [ Member] | Senior Notes [Member]
Derivative [Line Items]
Debt Instrument, Repurchased Face Amount | €					€ 42
Debt Instrument, Interest Rate, Stated Percentage	6.25%		6.25%	6.25%	6.25%
Gain (Loss) on Repurchase of Debt Instrument	$ (8)
Semi Annual Interest Rate Swap Payments By Counterparty | €				€ 302				€ 9
Short-term Debt, Refinanced, Description		$ 15	$ 403
Dollar Equivalent Interest Rate		7.491%
Derivative, Forward Exchange Rate | $ / €	1.0862	1.3325	1.1380	1.1380	1.0862			1.3325
Cash paid to purchase debt	$ (8)
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(52)		$ (43)
Derivative Assets (Liabilities), at Fair Value, Net	$ (52)		$ (43)
Other Contracts, A [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | Derivatives			1	1
Other Contracts, A [Member] | Minimum [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU			90
Credit Risk [Member]
Derivative [Line Items]
Number of counterparties in hedge facility | counterparty			13	13
Price Risk Derivative [Member] | Bilateral Hedging Agreement [Member]
Derivative [Line Items]
Multi-counterparty hedge facility, hedged total (in tcfe) | MMBoe			152.5	152.5
Basis Derivative [Member] | Bilateral Hedging Agreement [Member]
Derivative [Line Items]
Multi-counterparty hedge facility, hedged total (in tcfe) | MMBoe			6.5	6.5
Fair Value, Inputs, Level 3 [Member]
Derivative [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net			$ 269			$ 206
Fair Value, Inputs, Level 3 [Member] | Marketing, Gathering And Compression [Member] | Other Contracts, A [Member]
Derivative [Line Items]
Gains (losses) on undesignated oil and natural gas derivatives			$ 20