Net Income (Loss) Per Common Share - Calculations for Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net income (loss)—basic and diluted	$ 703	$ 909	$ 1,323	$ (317)
Denominator:
Basic weighted-average common shares outstanding (in shares)	161.1	160.8	161.1	161.5
Diluted weighted-average shares	162.9	161.5	162.7	161.5
Earnings (loss) per share:
Basic (in USD per share)	$ 4.36	$ 5.65	$ 8.21	$ (1.96)
Diluted (in USD per share)	$ 4.31	$ 5.63	$ 8.13	$ (1.96)
Number of anti-dilutive stock-based awards (in shares)	0.4	2.7	1.0	2.6
Cincinnati Global
Earnings (loss) per share:
Change in deferred tax assets	$ 3		$ 4
Change in deferred tax valuation allowance	$ 3		$ 4
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.2	0.3	1.0	0.0
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.6	0.4	0.6	0.0