Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Numerator:
Net income, as reported	$ 310	$ 267	$ 291	$ 248	$ 259	$ 274	$ 263	$ 232	$ 1,116	$ 1,029	$ 948
Less: Net income attributable to participating securities									(3)
Net income available to common shareholders									$ 1,113	$ 1,029	$ 948
Denominator:
Basic EPS- weighted average shares	133.26	136.74	141.79	144.80	148.49	151.33	152.04	154.55	139.11	151.59	164.48
Effect of dilutive securities:
Stock Options and SARS									0.24	0.20	0.14
Diluted EPS- adjusted weighted average shares and assumed conversions	133.56	137.02	141.96	144.94	148.76	151.54	152.22	154.72	139.35	151.79	164.62
Earning Per Share
Basic									$ 8.00	$ 6.78	$ 5.76
Diluted	$ 2.32	$ 1.94	$ 2.05	$ 1.71	$ 1.74	$ 1.81	$ 1.73	$ 1.50	$ 7.99	$ 6.78	$ 5.76
Earnings Per Share (Textual) [Abstract]
Common stock excluded from the diluted earnings per share									0.3	0.6	1.1