Employee Retirement Plans (Tables)

3 Months Ended

Mar. 31, 2012

Employee Retirement Plans [Abstract]

Components of net pension and postretirement benefits costs

	Three Months     ended March 31,
(millions)		2012	2011
Pension:
Service cost of benefits earned		$    8	$      7
Interest cost on projected benefit obligation		16	16
Expected return on plan assets		(17)	(16)
Net amortization		9	6
Net pension cost		$    16	$    13
Postretirement:
Service cost of benefits earned		$      1	$      2
Interest cost on projected benefit obligation		2	4
Net amortization		(9)	(6)
Net postretirement cost		$   (6)	$      -