Schedule II. Condensed Financial Information of Registrant (Condensed Statement of Cash Flows) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Net income	$ 744,959	$ 731,773	$ 760,790
Other, net	109,616	66,602	62,194
Cash provided from (used for) operating activities	1,437,680	1,476,434	1,363,874
Cash provided from (used for) investing activities:
Net decrease (increase) in short-term investments	38,637	(69,497)	34,003
Additions to properties	(38,244)	(41,756)	(42,203)
Cash provided from (used for) investing activities	(913,370)	(1,181,730)	(809,311)
Cash provided from (used for) financing activities:
Repayment of debt	(300,000)	(386,875)	(6,875)
Payment for debt issuance costs	(7,687)	(5,844)	0
Net issuance (repayment) of commercial paper	74,974	(34,445)	(11,610)
Issuance of stock	69,826	48,093	83,163
Acquisitions of treasury stock	(541,435)	(443,866)	(459,569)
Payment of dividends	(80,043)	(78,192)	(74,188)
Cash provided from (used for) financing activities	(523,603)	(274,057)	(590,508)
Net increase (decrease) in cash	(2,684)	18,914	(45,093)
Cash at beginning of year	94,847	75,933	121,026
Cash at end of year	92,163	94,847	75,933
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net income	744,959	731,773	760,790
Equity in earnings of affiliates	(788,768)	(760,329)	(810,596)
Cash dividends from subsidiaries	478,535	485,871	479,988
Other, net	58,617	21,129	65,584
Cash provided from (used for) operating activities	493,343	478,444	495,766
Cash provided from (used for) investing activities:
Net decrease (increase) in short-term investments	19,300	(15,899)	(3,380)
Investment in subsidiaries	(159,924)	(7,875)	0
Other long-term investments	(2,500)	0	0
Additions to properties	0	0	(32)
Loaned money to affiliates	(1,049,932)	(1,008,860)	(501,764)
Repayments from affiliates	1,200,932	782,860	501,764
Cash provided from (used for) investing activities	7,876	(249,774)	(3,412)
Cash provided from (used for) financing activities:
Repayment of debt	(300,000)	(386,875)	(6,875)
Proceeds from issuance of debt	325,000	700,000	0
Payment for debt issuance costs	(7,687)	(5,844)	0
Net issuance (repayment) of commercial paper	74,974	(34,445)	(11,610)
Issuance of stock	69,826	48,093	82,771
Acquisitions of treasury stock	(541,435)	(443,866)	(459,569)
Borrowed money from affiliate	32,000	76,000	277,000
Repayments to affiliates	(32,000)	(79,500)	(276,500)
Payment of dividends	(103,313)	(101,462)	(97,458)
Cash provided from (used for) financing activities	(482,635)	(227,899)	(492,241)
Net increase (decrease) in cash	18,584	771	113
Cash at beginning of year	1,644	873	760
Cash at end of year	$ 20,228	$ 1,644	$ 873