Affiliated companies and other equity-method investees - Summary of aggregate carrying amount and fair value of investments in affiliated companies and other equity-method investees (Detail) - Affiliated companies and other equity-method investees [Member] - JPY (¥) ¥ in Millions	Mar. 31, 2020	Mar. 31, 2019
Subsidiary or Equity Method Investee [Line Items]
Carrying amount	¥ 357,751	¥ 423,885
Fair value	¥ 511,667	¥ 600,132