Debt (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Debt Details [Abstract]
Commercial Paper Outstanding	$ 400	$ 200
Current maturities of long-term debt	0	1
Total short-term debt	400	201
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	4,995	4,986
Notes due 2016 2.75% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	600	600
Effective interest rate	2.75%	2.75%
Notes due 2017 5.375% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	250	250
Effective interest rate	5.375%	5.375%
Notes due 2018 6.35% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	131	131
Effective interest rate	6.35%	6.35%
Notes due 2019 8.5% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	251	251
Effective interest rate	8.50%	8.50%
Notes due 2020 4.375% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	249	249
Effective interest rate	4.375%	4.375%
Notes due 2020 5.125% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	299	299
Effective interest rate	5.125%	5.125%
Notes due 2021 6.37% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	78	78
Effective interest rate	6.37%	6.37%
Notes Due 2021 4.5% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	299	299
Effective interest rate	4.50%	4.50%
Notes due 2022 4% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	743	743
Effective interest rate	4.00%	4.00%
Notes due 2023 7.65% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	100	100
Effective interest rate	7.65%	7.65%
Notes due 2023 8.3% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	17	17
Effective interest rate	8.30%	8.30%
Debentures due 2027 7.875% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	300	300
Effective interest rate	7.875%	7.875%
Step Down Notes Due 2033 8.3% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	83	83
Effective interest rate	8.30%	8.30%
Notes due 2036 6.15% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	500	500
Effective interest rate	6.15%	6.15%
Notes Due 2041 5.875% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	298	298
Effective interest rate	5.875%	5.875%
Notes due 2042 5.375% Interest [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	750	750
Effective interest rate	5.375%	5.375%
Other Long Term Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	$ 47	$ 38