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Stock-based compensation plans (Details Textuals) (JPY ¥)
12 Months Ended
Mar. 31, 2011
Mar. 31, 2010
Mar. 31, 2009
Stock Based Compensation Plans (Additional Textuals) [Abstract]      
Number of shares to be issued on conversion of each Bond 100    
Stock-based compensation expense ¥ 1,952,000,000 ¥ 2,202,000,000 ¥ 3,446,000,000
Stock-based compensation expense related to income tax benefit 322,000,000 271,000,000 543,000,000
Total cash received from stock-based compensation plans 198,000,000 114,000,000 378,000,000
Stock Acquisition Rights Plan [Member]
     
Stock Based Compensation Plans (Textuals) [Abstract]      
Stock acquisition rights, vesting period 3 years    
Stock acquisition rights, maximum exercisable period 10 years    
Weighted-average fair value per share of stock acquisition rights granted ¥ 1,036 ¥ 813 ¥ 398
Total intrinsic value of shares exercised under stock acquisition rights plan 26,000,000 20,000,000 95,000,000
Nonvested Stock Acquisition Rights [Member]
     
Stock Based Compensation Plans (Textuals) [Abstract]      
Total unrecognized compensation expense related to nonvested stock acquisition rights 2,358,000,000    
Weighted-average period of total unrecognized compensation expense related to nonvested stock acquisition rights 1.99    
Total fair value of stock acquisition rights vested 1,921,000,000 2,136,000,000 3,333,000,000
Stock Appreciation Rights [Member]
     
Stock Based Compensation Plans (Textuals) [Abstract]      
Stock acquisition rights, vesting period 3 years    
Stock acquisition rights, maximum exercisable period 10 years    
Number of stock appreciation rights outstanding 45,425    
Weighted-average exercise price of stock appreciation rights ¥ 5,120