Portfolio of Available for Sale Debt Securities (Detail) ₨ in Millions, $ in Millions	Mar. 31, 2021 INR (₨)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 INR (₨)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	₨ 4,241,981.6	$ 57,998.1	₨ 3,340,732.3
Gross Unrealized Gains	57,061.0	780.2	68,285.4
Gross Unrealized Losses	23,592.7	322.6	2,728.5
Fair Value	4,275,449.9	58,455.7	3,406,289.2
Debt securities, other than asset and mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,084,551.2		3,213,339.7
Gross Unrealized Gains	52,977.7		66,538.4
Gross Unrealized Losses	23,281.0		2,578.5
Fair Value	4,114,247.9	$ 56,251.6	3,277,299.6
Debt securities, other than asset and mortgage-backed securities \| Government of India securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,159,905.2		2,637,464.4
Gross Unrealized Gains	31,824.6		52,630.0
Gross Unrealized Losses	20,225.8		1,491.6
Fair Value	3,171,504.0		2,688,602.8
Debt securities, other than asset and mortgage-backed securities \| State government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	348,067.7		177,055.9
Gross Unrealized Gains	7,373.7		11,337.7
Gross Unrealized Losses	2,669.6		0.0
Fair Value	352,771.8		188,393.6
Debt securities, other than asset and mortgage-backed securities \| Government securities outside India
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,932.2		8,367.0
Gross Unrealized Gains	3.8		48.4
Gross Unrealized Losses	0.0		0.0
Fair Value	5,936.0		8,415.4
Debt securities, other than asset and mortgage-backed securities \| Credit Substitutes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	534,227.1		360,741.5
Gross Unrealized Gains	13,423.1		2,309.5
Gross Unrealized Losses	373.3		677.3
Fair Value	547,276.9		362,373.7
Debt securities, other than asset and mortgage-backed securities \| Other corporate/financial institution bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	36,419.0		29,710.9
Gross Unrealized Gains	352.5		212.8
Gross Unrealized Losses	12.3		409.6
Fair Value	36,759.2		29,514.1
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30.5		37.3
Gross Unrealized Gains	1.8		0.8
Gross Unrealized Losses	0.0		0.0
Fair Value	32.3		38.1
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	157,399.9		125,931.2
Gross Unrealized Gains	4,081.5		1,746.0
Gross Unrealized Losses	311.7		150.0
Fair Value	161,169.7		127,527.2
Other securities (including mutual fund units)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			1,424.1
Gross Unrealized Gains			0.2
Gross Unrealized Losses			0.0
Fair Value			1,424.3
Securities with gross unrealized losses
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,162,099.9		300,932.1
Securities with gross unrealized gains
Schedule of Available-for-sale Securities [Line Items]
Fair Value	₨ 3,113,350.0		₨ 3,105,357.1

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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