Shareholders' Equity - Components of Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2023	Mar. 31, 2022
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock outstanding, beginning balance (in shares)		140,896,598			140,896,598
Shareholders' equity, beginning balance	$ 9,836,274	$ 9,419,091	$ 8,289,545	$ 7,906,889	$ 9,419,091	$ 7,906,889
Net income	357,671	271,860	324,999	249,209	629,531	574,208
Other comprehensive income (loss)	(30,333)	22,218	121,723	(45,947)	$ (8,115)	75,776
Cash dividends	(106,173)	(104,552)	(93,533)	(90,411)
Public and other stock offerings	143,814	223,779	336,469	265,861
Stock-based compensation plans	$ 3,952	3,878	4,028	3,944
Common stock outstanding, ending balance (in shares)	144,484,650				144,484,650
Shareholders' equity, ending balance	$ 10,205,205	$ 9,836,274	$ 8,983,231	$ 8,289,545	$ 10,205,205	$ 8,983,231
Cash dividends per share (USD per share)	$ 0.74	$ 0.74	$ 0.68	$ 0.68	$ 1.48	$ 1.36
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock outstanding, beginning balance (in shares)	143,155,761	140,896,598	135,425,081	132,419,754	140,896,598	132,419,754
Shareholders' equity, beginning balance	$ 716	$ 704	$ 677	$ 662	$ 704	$ 662
Public and other stock offerings (in shares)	1,316,930	2,147,210	3,509,116	2,730,115
Public and other stock offerings	$ 6	$ 11	$ 18	$ 13
Stock-based compensation plans (in shares)	11,959	111,953	77,832	275,212
Stock-based compensation plans		$ 1		$ 2
Common stock outstanding, ending balance (in shares)	144,484,650	143,155,761	139,012,029	135,425,081	144,484,650	139,012,029
Shareholders' equity, ending balance	$ 722	$ 716	$ 695	$ 677	$ 722	$ 695
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	6,065,763	5,838,118	5,293,541	5,023,751	5,838,118	5,023,751
Public and other stock offerings	143,808	223,768	336,451	265,848
Stock-based compensation plans	3,952	3,877	4,028	3,942
Shareholders' equity, ending balance	6,213,523	6,065,763	5,634,020	5,293,541	6,213,523	5,634,020
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	391,330	369,112	23,856	69,803	369,112	69,803
Other comprehensive income (loss)	(30,333)	22,218	121,723	(45,947)
Shareholders' equity, ending balance	360,997	391,330	145,579	23,856	360,997	145,579
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	3,378,465	3,211,157	2,971,471	2,812,673	3,211,157	2,812,673
Net income	357,671	271,860	324,999	249,209
Cash dividends	(106,173)	(104,552)	(93,533)	(90,411)
Shareholders' equity, ending balance	$ 3,629,963	$ 3,378,465	$ 3,202,937	$ 2,971,471	$ 3,629,963	$ 3,202,937