Fair Value Of Financial Instruments (Realized And Unrealized Gains And Losses Included In Earnings Pertaining To Level 3 Assets And Liabilities) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	$ 11	$ 13	$ 42	$ (26)
Variable Interest Entity Primary Beneficiary [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	4	(4)	(10)	34
Fair Value Inputs Level 3 [Member] | Total Gains (Losses) Included in Earnings [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gains (losses) on insured derivatives			0	(1)
Net gains (losses) on financial instruments at fair value and foreign exchange	4	(9)	13	(12)
Total revenues	7	(14)	0	17
Fair Value Inputs Level 3 [Member] | Change in Unrealized Gains (Losses) for the Period Included in Earnings for Assets and Liabilities still held [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gains (losses) on insured derivatives			0	(1)
Net gains (losses) on financial instruments at fair value and foreign exchange	4	(9)	13	(12)
Total revenues	8	(13)	15	21
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Total Gains (Losses) Included in Earnings [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	3	(5)	(13)	30
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Change in Unrealized Gains (Losses) for the Period Included in Earnings for Assets and Liabilities still held [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	$ 4	$ (4)	$ 2	$ 34