Property and Equipment - Additional Information (Detail) (USD $)	12 Months Ended					1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Assets Held under Capital Leases	Dec. 31, 2011 Assets Held under Capital Leases	Dec. 31, 2012 Corporate Headquarters Land and Buildings	Dec. 31, 2012 Corporate Headquarters Building Property	Dec. 31, 2012 Corporate Headquarters Land Property
Significant Acquisitions and Disposals [Line Items]
Payment to acquire property and equipment	$ 3,785,000,000	$ 1,811,000,000	$ 979,000,000			$ 1,200,000,000		$ 210,000,000
Number of property and equipment acquired							11	3
Property and equipment, estimated useful lives							40 years
Depreciation expense on fixed assets including amortization	1,653,000,000	1,034,000,000	552,000,000
Amortization of fixed assets acquired under capital lease obligations	510,000,000	335,000,000	164,000,000
Gross assets remaining under leases				2,300,000,000	1,600,000,000
Accumulated depreciation associated with leases				1,100,000,000	603,000,000
Cash paid for interest on capital leases	$ 51,000,000	$ 44,000,000	$ 26,000,000