Summary of significant accounting policies (Details 4)	12 Months Ended
Mar. 31, 2015 CNY (¥) ¥ / $ shares	Mar. 31, 2014 CNY (¥) shares	Mar. 31, 2013 CNY (¥)
Investment in equity investees
Period of time within which results of equity method earnings are recognized in arrears	3 months
Impairment charges of cost method investments	¥ 419,000,000	¥ 119,000,000	¥ 245,000,000
Impairment charges of equity method investments	¥ 438,000,000	¥ 0	0
Treasury shares
Number of ordinary shares included in treasury shares account \| shares	28,245,662	33,000,000
Statutory reserves
Percentage of after-tax profit from subsidiaries incorporated in the PRC required to be appropriated to the statutory reserves	10.00%
Limit of statutory reserve fund as a percentage of registered capital, after which allocations to statutory reserve fund are no longer required	50.00%
Convenience translation
Convenience exchange rate (RMB to USD) \| ¥ / $	6.1990
PRC
Statutory reserves
Appropriation to statutory reserves	¥ 267,000,000	¥ 1,137,000,000	241,000,000
Appropriation to the enterprise expansion fund and staff welfare and bonus fund	0	0	0
Interest rate swaps
Interest rate swaps
Loss recorded in consolidated income statements upon termination of the interest rate swaps contracts	59,000,000
Gain (loss) on the fair value change of the interest rate swaps not qualified for hedge accounting	¥ (43,000,000)	¥ 102,000,000	¥ 0

Amount appropriated to the enterprise expansion fund and staff welfare and bonus fund for entities incorporated in PRC.

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Amount appropriated from retained earnings to statutory reserves for entities incorporated in PRC.

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Represents the minimum percentage of net income from required to be appropriated towards the statutory reserve fund for entities incorporated in the People's Republic of China until the reserve balance reaches 50 percent of registered capital.

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Represents the exchange rate used for convenience translation from reporting currency to additional disclosures in another currency.

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Represents the period of time within which the results of equity method earnings are recognized in arrears.

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Represents the level of the statutory reserve fund balance as a percentage of registered capital for entities incorporated in the People's Republic of China which must be attained before mandatory transfers to the reserve are no longer required.

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This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the cost method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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Amount of gain (loss) included in earnings for the period from the increase (decrease) in fair value of interest rate derivatives not designated as hedging instruments.

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The amount of net gains or losses on interest rate cash flow hedges reclassified during the period to earnings from accumulated other comprehensive income upon the hedged transaction affecting earnings.

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Number of shares held for each class of treasury stock.

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