The following table summarizes certain significant costs and expenses that require management estimates for the three years ended December 31, 2013:



	Year Ended December 31,
Expense/(Income)	2013			2012			2011
Provisions for restructuring and asset impairments	$	116		$	154		$	32
Provisions for receivables	123			127			154
Provisions for litigation and regulatory matters	(34		)	(1		)	11
Provisions for obsolete and excess inventory	35			30			39
Provisions for product warranty liability	28			29			30
Depreciation and obsolescence of equipment on operating leases	283			279			294
Depreciation of buildings and equipment	431			452			405
Amortization of internal use software	147			116			91
Amortization of product software	43			19			11
Amortization of acquired intangible assets	332			328			401
Amortization of customer contract costs	122			107			49
Defined pension benefits - net periodic benefit cost⁽¹⁾	267			300			177
Retiree health benefits - net periodic benefit cost	1			11			14
Income tax expense	276			272			377

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(1)	2011 includes $107 pre-tax curtailment gain - refer to Note 15 - Employee Benefit Plans for additional information.