Debt (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Debt Details [Abstract]
Commercial Paper Outstanding	$ 200	$ 100
Current maturities of long-term debt	1	4
Total short-term debt	201	104
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	4,986	4,990
Net proceeds on issuance of long-term debt	0	2,676	543
Debt Tender Details [Abstract]
Repayments Of Debt		449
Maturities Of Debt and Capital Leases [Abstract]
Future Maturities of Debt and Capital Leases in 2012	1
Future Maturities of Debt and Capital Leases in 2013	23
Future Maturities of Debt and Capital Leases in 2014	0
Future Maturities of Debt and Capital Leases in 2015	600
Future Maturities of Debt and Capital Leases in 2016	250
Future Maturities of Debt and Capital Leases for Years After 2016	remainder
Interest Expense [Abstract]
Interest Expense on Long-term Debt, Short-term Debt and Capital Leases	268	202	182
Unsecured Debt [Member] | Proceeds from debt used to fund acquisition [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	2011-11-10
Long Term Debt Face Value	2,100
Notes due 2016 2.75% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	600	600
Notes due 2016 2.75% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Nov. 15, 2016
Long Term Debt Face Value	600
Stated interest rate	2.75%
Effective interest rate	2.936%
Percentage of principal amount to be paid upon redemption	100.00%
Basis Points Added To Treasury Rate	30
Notes due 2016 2.75% Interest [Member] | Unsecured Debt [Member] | Proceeds from debt used to fund acquisition [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	2011-11-10
Notes due 2017 5.375% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	250	250
Notes due 2017 5.375% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Stated interest rate	5.375%
Notes due 2018 6.35% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	131	131
Notes due 2018 6.35% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Stated interest rate	6.35%
Basis Points Added To Treasury Rate			45
Debt Tender Details [Abstract]
Tender Offer Price And Discount Rate			The tender price equaled the present value of the remaining principal and interest payments on the Notes being redeemed, discounted at a rate equal to the 10 year Treasury rate plus a fixed spread of 45 basis points.
Debt Tender Pricing Yield			3.923%
Amount Of Debt Tendered			169
Repayments Of Debt			198
Gain (loss) on extinquishment of debt, net of tax			18
Notes due 2019 8.5% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	251	251
Debt Tender Details [Abstract]
Debt Tender Pricing Yield			4.128%
Notes due 2019 8.5% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Stated interest rate	8.50%
Basis Points Added To Treasury Rate			100.00
Debt Tender Details [Abstract]
Tender Offer Price And Discount Rate			The tender price equaled the present value of the remaining principal and interest payments on the Notes being redeemed, discounted at a rate equal to the 10 year Treasury rate plus a fixed spread of 100 basis points.
Amount Of Debt Tendered			99
Repayments Of Debt			130
Gain (loss) on extinquishment of debt, net of tax			21
Notes due 2020 4.375% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	249	249
Percentage of principal amount to be paid upon redemption	100.00%
Basis Points Added To Treasury Rate	25
Notes due 2020 4.375% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Long Term Debt Face Value	250
Stated interest rate	4.375%
Effective interest rate	5.10%
Notes due 2020 5.125% Interest [Member]
Debt Instrument [Line Items]
Long Term Debt Face Value		300
Long-term Debt, Excluding Current Maturities	299	299
Percentage of principal amount to be paid upon redemption	100.00%
Basis Points Added To Treasury Rate	25
Notes due 2020 5.125% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Jun. 15, 2020
Stated interest rate	5.125%
Effective interest rate	5.36%
Notes due 2021 6.37% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	78	78
Notes due 2021 6.37% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Stated interest rate	6.37%
Notes Due 2021 4.5% Interest [Member]
Debt Instrument [Line Items]
Long Term Debt Face Value	300
Long-term Debt, Excluding Current Maturities	299	298
Notes Due 2021 4.5% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Mar. 15, 2021
Stated interest rate	4.50%
Effective interest rate	4.683%
Percentage of principal amount to be paid upon redemption	100.00%
Basis Points Added To Treasury Rate	20
Notes due 2022 4% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	743	743
Notes due 2022 4% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Feb. 15, 2022
Long Term Debt Face Value	750
Stated interest rate	4.00%
Effective interest rate	4.346%
Percentage of principal amount to be paid upon redemption	100.00%
Basis Points Added To Treasury Rate	35
Notes due 2022 4% Interest [Member] | Unsecured Debt [Member] | Proceeds from debt used to fund acquisition [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	2011-11-10
Notes due 2023 7.65% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	100	100
Notes due 2023 7.65% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Stated interest rate	7.65%
Notes due 2023 8.3% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	17	17
Notes due 2023 8.3% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Stated interest rate	8.30%
Debentures due 2027 7.875% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	300	300
Debentures due 2027 7.875% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Stated interest rate	7.875%
Step Down Notes Due 2033 8.3% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	83	83
Step Down Notes Due 2033 8.3% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Stated interest rate	8.30%
Notes due 2036 6.15% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	500	500
Notes due 2036 6.15% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Stated interest rate	6.15%
Notes Due 2041 5.875% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	298	298
Notes Due 2041 5.875% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Mar. 15, 2041
Long Term Debt Face Value	300
Stated interest rate	5.875%
Effective interest rate	6.008%
Percentage of principal amount to be paid upon redemption	100.00%
Basis Points Added To Treasury Rate	25
Notes due 2042 5.375% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	750	750
Notes due 2042 5.375% Interest [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Feb. 15, 2042
Long Term Debt Face Value	750
Stated interest rate	5.375%
Effective interest rate	5.542%
Percentage of principal amount to be paid upon redemption	100.00%
Basis Points Added To Treasury Rate	40
Notes due 2042 5.375% Interest [Member] | Unsecured Debt [Member] | Proceeds from debt used to fund acquisition [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	2011-11-10
Other Long Term Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	$ 38	$ 43