Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		1 Months Ended		9 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Feb. 29, 2012 Revolving Credit Facility	Feb. 29, 2012 Bridge Loan	Sep. 30, 2012 Minimum	Feb. 29, 2012 Minimum Bridge Loan	Sep. 30, 2012 Maximum	Feb. 29, 2012 Maximum Bridge Loan	Sep. 30, 2012 Buildings	Oct. 24, 2012 Subsequent Event Unsecured Term Loan
Leases [Abstract]
Capital lease agreement period			3 years								15 years
Interest rate							1.00%		13.00%
Expiration date of lease							2012		2027
Operating lease expense	$ 50	$ 52	$ 151	$ 171
Credit Facilities [Abstract]
Credit facility, maturity period					5 years							3 years
Line of credit facility, maximum borrowing capacity					$ 5,000	$ 3,000						$ 1,500
Interest payable on borrowed amounts					1.00%	1.00%						1.00%
Commitment fee payable per annum on daily undrawn balance					0.10%	0.10%						0.10%
Interest payable on undrawn outstanding balances						0.25%
Expiration period								1 year
Expiration date										2014-06-30
Minimum number of days after borrowing to pay additional interest on drawn balances outstanding						180 days
Minimum number of days after entering bridge facility to pay commitment fee on daily undrawn balance						90 days