Capitalization - Additional Information (Details) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 06, 2023 USD ($) $ / shares	Mar. 31, 2023 USD ($) dealer $ / shares	Jun. 30, 2023 USD ($) shares	Mar. 31, 2023 USD ($) $ / shares	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) shares	Dec. 31, 2023 USD ($)	Feb. 28, 2023 USD ($)
Debt Instrument [Line Items]
Number of dealers | dealer		2
Authorized repurchased amount		$ 1,000		$ 1,000
Par value (in usd per share) | $ / shares		$ 0.10		$ 0.10
Repurchase of common shares					$ 1,000	$ 0	$ 1,000
Shares repurchased (in shares) | shares			1,812,497				8,730,766
Par value of shares acquired (in usd per share) | $ / shares	$ 91.63
Common stock repurchases	$ 800		$ 2	$ 1,008
Adjustment to APIC	$ 200
Adjustments to APIC reflecting fair value of common shares issued			$ 169
5.20% Debentures Due 2033 | Debentures
Debt Instrument [Line Items]
Long-term debt									$ 500
Interest rate (percent)									5.20%
6.59% Debentures Due 2033 | Debentures | O&R | Scenario, Forecast
Debt Instrument [Line Items]
Long-term debt								$ 50
Interest rate (percent)								6.59%