Fair Value (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Cash and Cash Equivalents:
Total cash and cash equivalents	$ 1,634	$ 2,063	$ 1,384	$ 1,191
Fair value measurements, Recurring [Member]
Cash and Cash Equivalents:
Prime money market funds	1,634	2,063
Total cash and cash equivalents	1,634	2,063
Derivative Asset:
Total derivative instruments	95
Derivative Liability:
Total derivative liability		19
Fair value measurements, Recurring [Member] | Level 1 [Member]
Cash and Cash Equivalents:
Prime money market funds	1,634	2,063
Total cash and cash equivalents	1,634	2,063
Derivative Asset:
Total derivative instruments	0
Derivative Liability:
Total derivative liability		0
Fair value measurements, Recurring [Member] | Level 2 [Member]
Cash and Cash Equivalents:
Prime money market funds	0	0
Total cash and cash equivalents	0	0
Derivative Asset:
Total derivative instruments	95
Derivative Liability:
Total derivative liability		19
Fair value measurements, Recurring [Member] | Level 3 [Member]
Cash and Cash Equivalents:
Prime money market funds	0	0
Total cash and cash equivalents	0	0
Derivative Asset:
Total derivative instruments	0
Derivative Liability:
Total derivative liability		0
Interest rate swaps - fixed to floating rate [Member] | Fair value measurements, Recurring [Member]
Derivative Asset:
Total derivative instruments	95
Derivative Liability:
Total derivative liability		19
Interest rate swaps - fixed to floating rate [Member] | Fair value measurements, Recurring [Member] | Level 1 [Member]
Derivative Asset:
Total derivative instruments	0
Derivative Liability:
Total derivative liability		0
Interest rate swaps - fixed to floating rate [Member] | Fair value measurements, Recurring [Member] | Level 2 [Member]
Derivative Asset:
Total derivative instruments	95
Derivative Liability:
Total derivative liability		19
Interest rate swaps - fixed to floating rate [Member] | Fair value measurements, Recurring [Member] | Level 3 [Member]
Derivative Asset:
Total derivative instruments	0
Derivative Liability:
Total derivative liability		$ 0