Business Combinations (Details) In Millions, except Share data in Billions, unless otherwise specified	3 Months Ended
	Jun. 30, 2012 ERA Mining Machinery Limited USD ($) Y types	Jun. 30, 2012 ERA Mining Machinery Limited Cash Consideration HKD	Jun. 30, 2012 ERA Mining Machinery Limited Loan note consideration HKD	Mar. 31, 2012 Caterpillar Tohoku Limited USD ($)
Business Acquisition
Percentage of equity acquired (as a percent)	99.00%			100.00%
Percentage of issued shares outstanding and unacquired (as a percent)	1.00%
Purchase price of acquired entity	$ 690			$ 202
Cost of acquisition, net cash paid	453
Cost of acquisition paid in cash	475			59
Cash acquired	22			18
Far value of loan notes issued for shares	169
Third party liabilities assumed	155			77
Loan and Interest Payable to Caterpillar	51
Restricted cash acquired	138
Fair value of noncontrolling interest	7
Loan notes debt component, minimum redemption amount	152
Loan notes, fair value of contingent consideration	17
Trade payables acquired due to Caterpillar				64
Estimated consideration payable				21
Business Combination, Alternate considerations to acquiree
Number of consideration alternatives	2
Value of Consideration to be paid (in HKD/share)		0.88	1.00
Contingent consideration arrangement, value minimum (in HKD/share)			0.75
Contingent consideration arrangement, value maximum (HKD/share)			1.15
Number of shares tendered (in shares)		4.0	1.6
Assets
Tangible assets acquired	671			251
Cash acquired	22			18
Restricted cash acquired	138
Receivables trade and other	213			33
Inventory	105			26
Property, plant and equipment	112			157
Finite-lived intangible assets	194			8
Goodwill	467			16
Finite-lived Intangible Asset, Weighted Average Useful Life (in years)	15
Liabilities
Total liabilities assumed	592			132
Accounts payable	342			39
Third party liabilities assumed	155			77
Accrued expenses	50
Deferred Income Tax Liability	$ 38