Summary by Business Segment (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Segment Reporting Information [Line Items]
Number Of Business Segments	2
Revenues derived from foreign countries	$ 84	$ 83	$ 75
Long-lived assets attributable to foreign operations	$ 157	$ 146	$ 142
Percentage of total sales of largest customer	0.50%
Distribution Business Segment [Member]
Segment Reporting Information [Line Items]
Number of Operating Segments	19
Sales Revenue, Gas and Rent Percentage	59.00%	58.00%	60.00%
Sales Revenue, Hardgoods Percentage	41.00%	42.00%	40.00%
Revenues from distribution segment, Percentage	90.00%	90.00%	90.00%
All Other Operations Business Segment [Member]
Segment Reporting Information [Line Items]
Number of Operating Segments	6
Maximum [Member]
Segment Reporting Information [Line Items]
Long-lived assets in foreign countries as percentage of consolidated total long-lived assets	4.00%
Carbon dioxide, dry ice, nitrous oxide, ammonia and refrigerant gases [Member] | All Other Operations Business Segment [Member]
Segment Reporting Information [Line Items]
Number of Operating Segments	5
Medical gas system construction and service business [Member] | All Other Operations Business Segment [Member]
Segment Reporting Information [Line Items]
Number of Operating Segments	1