Contingencies and Commitments (Schedule of Future Payments for Driling Contracts table) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 181
Operating Leases, Future Minimum Payments, Due in Two Years	220
Operating Leases, Future Minimum Payments, Due in Three Years	99
Operating Leases, Future Minimum Payments Due	768
Drilling Rigs
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	123
Operating Leases, Future Minimum Payments, Due in Two Years	68
Operating Leases, Future Minimum Payments, Due in Three Years	11
Operating Leases, Future Minimum Payments Due	$ 202