Contingencies and Commitments Contingencies - Drilling Contracts (Details) - Drilling Rig Leases [Member] $ in Millions	Dec. 31, 2016 USD ($)
Other Commitments [Line Items]
Contractual Obligation, Due in Next Fiscal Year	$ 91
Contractual Obligation, Due in Second Year	14
Contractual Obligation	$ 105

Amount of contractual obligation due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

No definition available.

Name:	us-gaap_ContractualObligationDueInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant