Investments (Portion Of Unrealized Gains And Losses On Equity Investments Held) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Gain (Loss) on Investments [Line Items]
Realized investment gains (losses)			$ (6)	$ (3)
Equity and Trading securities [Member] \| Net gains (losses) recognized during the period on equity and trading securities [Member]
Gain (Loss) on Investments [Line Items]
Realized investment gains (losses)	$ 4	$ (56)	1	(58)
Equity and Trading securities [Member] \| Net gains (losses) recognized during the period on equity and trading securities sold during the period [Member]
Gain (Loss) on Investments [Line Items]
Realized investment gains (losses)	0	1	2	1
Equity and Trading securities [Member] \| Unrealized gains (losses) recognized during the period on equity and trading securities still held at the reporting date [Member]
Gain (Loss) on Investments [Line Items]
Realized investment gains (losses)	$ 4	$ (57)	$ (1)	$ (59)