Pensions and Other Postretirement Benefits (Net Periodic Benefit Costs) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012 Pensions	Dec. 31, 2011 Pensions	Dec. 31, 2012 Pensions Defined Contribution Pension	Dec. 31, 2011 Pensions Defined Contribution Pension	Dec. 31, 2010 Pensions Defined Contribution Pension	Dec. 31, 2012 Pensions Other Postretirement Benefits	Dec. 31, 2011 Pensions Other Postretirement Benefits	Dec. 31, 2010 Pensions Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 61	$ 63	$ 61	$ 63	$ 64	$ 22	$ 19	$ 19
Interest cost		239	254	239	254	249	57	63	64
Expected return on plan assets				(292)	(312)	(278)
Amortization of prior service cost (credit)		0			1	5	(12)	(12)	(5)
Amortization of actuarial losses		139		151	120	121	34	30	19
Curtailments and special termination benefits	30	6	58		5
Net periodic benefit cost				$ 159	$ 131	$ 161	$ 101	$ 100	$ 97