Long-term Debt and Capital Lease Obligations Annual Maturities of Long-term Debt and Capital Lease Obligations (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Unamortized discount	$ (14)
Carrying Value	6,806	6,157
Amounts representing interest	(60)
Long-term Debt Repayments of Principal and Capital Leases Future Minimum Payments in Next Twelve Months	273
Long-term Debt Repayments of Principal and Capital Leases Future Minimum Payments Due in Two Years	261
Long-term Debt Repayments of Principal and Capital Leases Future Minimum Payments Due in Three Years	129
Long-term Debt Repayments of Principal and Capital Leases Future Minimum Payments Due in Four Years	64
Long-term Debt Repayments of Principal and Capital Leases Future Minimum Payments Due in Five Years	63
Long-term Debt Repayments of Principal and Capital Leases Future Minimum Payments Due Thereafter	6,145
Total Long-term Debt Maturities and Capital Leases Future Minimum Payments	6,935
Total long-term debt and capital lease obligations	6,861	6,213
Long-term Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	261
Long-term Debt, Maturities, Repayments of Principal in Year Two	253
Long-term Debt, Maturities, Repayments of Principal in Year Three	122
Long-term Debt, Maturities, Repayments of Principal in Year Four	57
Long-term Debt, Maturities, Repayments of Principal in Year Five	52
Long-term Debt, Maturities, Repayments of Principal after Year Five	6,075
Principal Amount	6,820
Unamortized discount	(14)
Carrying Value	6,806
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	12
Capital Leases, Future Minimum Payments Due in Two Years	8
Capital Leases, Future Minimum Payments Due in Three Years	7
Capital Leases, Future Minimum Payments Due in Four Years	7
Capital Leases, Future Minimum Payments Due in Five Years	11
Capital Leases, Future Minimum Payments Due Thereafter	70
Capital Leases, Future Minimum Payments Due	115
Amounts representing interest	(60)
Capital Lease Obligations	$ 55