Long-term debt (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Jun. 30, 2010	May 23, 2011	Dec. 31, 2010
Debt Instrument
Aggregate principal amount of fixed and floating rate long-term debt				$ 3,500,000,000
Proceeds from Issuance of Long-term Debt		3,497,000,000	0
Payments of Debt Issuance Costs		12,000,000	0
Long-term Debt
Less unamortized discount	(2,000,000)	(2,000,000)
Total long-term debt	3,498,000,000	3,498,000,000			0
Redemption of fixed-rate debt as a percentage of its aggregate principal amount	101.00%
Notes Payable | $1.0 billion floating-rate notes due 2013 (swapped to a 0.922% fixed rate)
Long-term Debt
Long-term Debt, Gross	1,000,000,000	1,000,000,000
Notes Payable | $500 million 0.875% notes due 2013
Long-term Debt
Long-term Debt, Gross	500,000,000	500,000,000
Notes Payable | $1.0 billion 1.375% notes due 2014
Long-term Debt
Long-term Debt, Gross	1,000,000,000	1,000,000,000
Notes Payable | $1.0 billion 2.375% notes due 2016
Long-term Debt
Long-term Debt, Gross	1,000,000,000	1,000,000,000
Fixed Rate
Long-term Debt
Fixed-rate Long-term Debt, Subject to Mandatory Redemption	$ 2,500,000,000	$ 2,500,000,000
$1.0 billion floating-rate notes due 2013 (swapped to a 0.922% fixed rate) | Interest Rate Swap | Cash Flow Hedges
Debt Instrument
Long-term debt, effective fixed-rate interest rate	0.922%	0.922%
$500 million 0.875% notes due 2013
Debt Instrument
Long-term debt, stated interest rate	0.875%	0.875%
$1.0 billion 1.375% notes due 2014
Debt Instrument
Long-term debt, stated interest rate	1.375%	1.375%
$1.0 billion 2.375% notes due 2016
Debt Instrument
Long-term debt, stated interest rate	2.375%	2.375%