Investments Composition of Fixed Maturities by Maturity (Detail) - Total fixed maturities $ in Millions	Mar. 31, 2022 USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Less than one year	$ 5,702.8
One to five years	29,007.2
Five to ten years	13,251.5
Ten years or greater	121.2
Cost	48,082.7
Fair Value
Less than one year	5,670.9
One to five years	28,094.9
Five to ten years	12,430.7
Ten years or greater	119.9
Fair Value	$ 46,316.4

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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