Employee benefit plans - Amounts in Accumulated other comprehensive income, pre-tax, expected to be recognized as components of net periodic benefit cost over next fiscal year (Detail) ¥ in Millions	12 Months Ended
Mar. 31, 2017 JPY (¥)
Employee benefit plans
Net actuarial loss	¥ 3,950
Net prior service cost	(1,148)
Total	¥ 2,802

Amount included in accumulated other comprehensive income (AOCI) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position, including gain (loss), prior service cost (credit), and transition asset (obligation).

No definition available.

Name:	us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration