Share-based compensation plans (Tables)

12 Months Ended

Dec. 31, 2011

Share-based compensation plans [Abstract]

Option Activity [Table Text Block]

							Weighted-Average			Aggregate
		Shares			Weighted- Average		Remaining Contractual			Intrinsic Value
		(in thousands)			Exercise Price Per Share		Term (in years)			(in millions)
Outstanding at December 31, 2008		3,322		$	28.95
Granted		289			27.59
Exercised		(79)			16.50
Forfeited or expired		(97)			34.08
Outstanding at December 31, 2009		3,435			28.98
Granted		367			19.05
Exercised		(372)			17.50
Forfeited or expired		(75)			31.71
Outstanding at December 31, 2010		3,355			29.10
Granted		290			31.47
Exercised		(562)			20.66
Forfeited or expired		(116)			29.47
Outstanding at December 31, 2011
			2,967		$	30.92		2.5		$	3.0
Of the above, as of December 31, 2011:
	Exercisable	2,397		$	32.03		1.9		$	1.4
	Expected to vest in future periods (a)	555		$	26.18		4.8		$	1.6

Fair value of options calculation assumptions [Table Text Block]

				Years Ended December 31,
				2011			2010			2009
Number of shares underlying options, in thousands						290			367			289
Weighted-average exercise price per share			$			31.47			19.05			27.59
Assumptions used to estimate fair value
	Expected dividend yield (a):
		Weighted-average				1.3%			2.1%			1.4%
	Expected volatility (b):
		Weighted-average				36%			36%			36%
		Range		36%	–	37%	35%	–	39%	35%	–	39%
	Risk-free interest rate (c):
		Weighted-average				1.2%			1.4%			1.8%
		Range		0.5%	–	1.9%	0.6%	–	1.9%	0.9%	–	2.4%
	Expected term in years (d):
		Weighted-average				3.8			3.8			3.8
		Range		1.9	–	5.3	1.9	–	5.3	1.9	–	5.3
Weighted-average fair value estimates at grant date:
	In millions		$			2.4			1.7			2.1
	Fair value per share		$			8.17			4.65			7.24

Nonvested share activity [Table Text Block]

Nonvested Share Activity
		Number of shares				Weighted-Average
		2005	Directors’			Grant-Date
(in thousands of shares, except per share amounts)		Plan	Plan	Total		Fair Value (a)
Balance as of January 1, 2009		55.6	15.3	70.9	$	36.27
Granted		178.4	22.7	201.1		26.90
Cancelled awards		(1.3)	-	(1.3)		26.80
Vested		(18.5)	(15.3)	(33.8)		35.71
	Balance as of December 31, 2009	214.2	22.7	236.9		28.45
Granted		167.6	29.1	196.7		19.24
Cancelled awards		(5.6)	-	(5.6)		22.52
Vested		(76.7)	(22.7)	(99.4)		29.12
	Balance as of December 31, 2010	299.5	29.1	328.6		22.84
Granted		143.7	15.8	159.5		30.43
Cancelled awards		(16.5)	-	(16.5)		23.65
Vested		(127.1)	(29.1)	(156.2)		24.13
	Balance as of December 31, 2011	299.6	15.8	315.4	$	25.99