Reclassifications of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit		$ 38,360	$ 33,172	$ 88,013	$ 97,305
Net income		115,770	99,046	321,445	293,869
Interest expense		$ 136,163	$ 218,636	489,941	$ 639,547
Reclassifications, net of tax	[1]			(7,697)
Past service liability
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, before tax	[1],[2]			186
Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, before tax	[1],[2]			(5,511)
Amortization of defined benefit pension
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, before tax	[1]			(5,325)
Tax benefit	[1]			1,464
Reclassifications, net of tax	[1]			(3,861)
Reclassification out of Accumulated Other Comprehensive Income (loss) | Unrealized gains on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities	[1]			683
Income tax (expense) benefit	[1]			(188)
Net income	[1]			495
Reclassification out of Accumulated Other Comprehensive Income (loss) | Unrealized loss on cash flow hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit	[1]			1,642
Net income	[1]			(4,331)
Interest expense	[1]			$ (5,973)

[1] Amounts in parentheses indicate expense items.

[2] See Note 8, “Pension and Other Post-Retirement Benefits,” for additional information.