Other comprehensive income (loss) - Changes in Accumulated other comprehensive income (loss) (Parenthetical) (Detail) - Reclassifications out of accumulated other comprehensive income (loss) [Member] - Cumulative translation adjustments [Member] ¥ in Millions	6 Months Ended
	Sep. 30, 2020 JPY (¥)
Affected line items in consolidated statements of income [Line Items]
Reclassification adjustment for profit (loss)	¥ 12,846
Amount of income tax loss allocated to reclassification adjustment	¥ 2,145