Accrued Expenses and Allowance for Doubtful Accounts - Summary of Other Accrued Expenses (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Accrued Liabilities [Line Items]
Professional liability risks	$ 324	$ 298
Interest	409	383
Taxes other than income	235	232
Legal claim costs	175
Other	706	672
Other accrued expenses	$ 1,849	$ 1,585