Income Taxes - Valuation Allowances (Details) - USD ($) $ in Millions	Mar. 31, 2025	Mar. 31, 2024
Valuation Allowance [Line Items]
Deferred tax assets, impairment of equity securities and other unrealized investment losses.	$ 856
Impairment of equity securities \| Equity securities
Valuation Allowance [Line Items]
Deferred tax assets, valuation allowance	$ 636	$ 427

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-2

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant