Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 15,945,105	$ 15,691,827	$ 15,716,649	$ 15,460,191
Net gain during period	(69,127)	32,650	382,183	339,773
Ending balance	16,101,013	15,779,811	16,101,013	15,779,811
Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			37,380
Net gain during period			114,451
Ending balance	151,831		151,831
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(342,419)
Net gain during period			27,431
Ending balance	(314,988)		(314,988)
Cash Flow Hedges and Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			98,359
Net gain during period			240,301
Ending balance	338,660		338,660
Accumulated Other Comprehensive Income (Loss), Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	244,630	(112,958)	(206,680)	(420,081)
Net gain during period			382,183
Ending balance	$ 175,503	$ (80,308)	$ 175,503	$ (80,308)