Income Taxes - Tax Cost Basis and Estimated Aggregate Gross Unrealized Gain (Loss) on Investments for Federal Income Tax Purposes (Details) - U.S. Federal Income Tax - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Income Taxes Disclosure [Line Items]
Tax cost on investments	$ 1,062,910	$ 1,105,481
Change in unrealized gain on a tax basis	10,414	11,239
Change in unrealized loss on a tax basis	(56,992)	(49,711)
Net unrealized gain (loss) on a tax basis	$ (46,578)	$ (38,472)