Long-Term Debt - Outstanding Long-Term Debt- Supplemental Information (Detail)	9 Months Ended
	Sep. 30, 2021
9.08% bond, due June 1, 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Jun. 01, 2022
Debt Instrument, Interest Rate, Stated Percentage	9.08%
5.50% note, due October 12, 2020 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Oct. 12, 2020
Debt Instrument, Interest Rate, Stated Percentage	5.50%
5.93% note, due October 31, 2023 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Oct. 31, 2023
Debt Instrument, Interest Rate, Stated Percentage	5.93%
5.68% note, due June 30, 2026 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Jun. 30, 2026
Debt Instrument, Interest Rate, Stated Percentage	5.68%
6.43% note, due May 2, 2028 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	May 02, 2028
Debt Instrument, Interest Rate, Stated Percentage	6.43%
3.73% note, due December 16, 2028 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Dec. 16, 2028
Debt Instrument, Interest Rate, Stated Percentage	3.73%
3.88% note, due May 15, 2029 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	May 15, 2029
Debt Instrument, Interest Rate, Stated Percentage	3.88%
3.25% due April 30, 2032 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Apr. 30, 2032
Debt Instrument, Interest Rate, Stated Percentage	3.25%
3.48% note, due May 31, 2038 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	May 31, 2038
Debt Instrument, Interest Rate, Stated Percentage	3.48%
Uncollateralized Senior Note Due November Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Nov. 30, 2038
Debt Instrument, Interest Rate, Stated Percentage	3.58%
Uncollateralized Senior Note Due August Two Thousand Thirty Nine [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Aug. 20, 2039
Debt Instrument, Interest Rate, Stated Percentage	3.98%
Uncollateralized Senior Note Due December Two Thousand Thirty Four [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Dec. 20, 2034
Debt Instrument, Interest Rate, Stated Percentage	2.98%
Uncollateralized Senior Note Due July Two Thousand Thirty Five
Debt Instrument [Line Items]
Debt instrument, maturity date	Jul. 15, 2035
Debt Instrument, Interest Rate, Stated Percentage	3.00%
Uncollateralized Senior Note Due August Two Thousand Thirty Five
Debt Instrument [Line Items]
Debt instrument, maturity date	Aug. 15, 2035
Debt Instrument, Interest Rate, Stated Percentage	2.96%
Equipment Security Note
Debt Instrument [Line Items]
Debt instrument, maturity date	Sep. 29, 2031
Debt Instrument, Interest Rate, Stated Percentage	2.46%