Business Acquisitions - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		7 Months Ended	12 Months Ended
	May 23, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill, Purchase Accounting Adjustments					$ 0	$ (2)
Goodwill				$ 1,913	1,911	1,911	$ 1,913
Reinsurance premium					0	0	91
Revenues					22,390	20,523	20,740
Net income (loss) available to common stockholders					2,344	1,716	2,064
Net investment income					2,313	1,846	1,951
Adverse Development Cover Navigators Group [Member]
Business Acquisition [Line Items]
Reinsurance premium	$ 91
Adverse development from comprehensive annual review					300
Change in Deferred Gain on Retroactive Reinsurance					91	102	16
Adverse Development Cover Navigators Group [Member] | Maximum
Business Acquisition [Line Items]
Reinsurance Retention Policy, Excess Retention, Amount Reinsured					300
Adverse Development Cover Navigators Group [Member] | Retention Layer Above Reserve for the Covered Liabilities as of the Inception Date [Member]
Business Acquisition [Line Items]
Reinsurance Retention Policy, Amount Retained					100
Adverse Development Cover Navigators Group [Member] | Retention Layer for Reserve for the Covered Liabilities as of the Inception Date [Member]
Business Acquisition [Line Items]
Reinsurance Retention Policy, Amount Retained					$ 1,816
The Navigators Group, Inc. [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	May 23, 2019
Business Acquisition, Name of Acquired Entity	Navigators Group
Business Acquisition, Share Price	$ 70
Payments to Acquire Businesses, Gross	$ 2,121
Business Combination, Consideration Transferred, Other	23
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Total Assets		$ 9
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Total Liabilities		7
Goodwill, Purchase Accounting Adjustments		$ (2)
Goodwill	623					$ 621
Revenues				1,000
Net income (loss) available to common stockholders				167
Net investment income				67
Net Investment Income, after Tax				54
Business Combination, Acquisition Related Costs							17
The Navigators Group, Inc. [Member] | Adverse Development Cover Navigators Group [Member]
Business Acquisition [Line Items]
Reinsurance premium				91			91
Reinsurance Retention Policy, Amount Retained			$ 68				68
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims			97	97			84
Current accident year			$ 29
Use of Retention Layer by Acquiree Prior to Acquisition	32
Adverse development from comprehensive annual review							91
Change in Deferred Gain on Retroactive Reinsurance				16
The Navigators Group, Inc. [Member] | Adverse Development Cover Navigators Group [Member] | After tax [Member]
Business Acquisition [Line Items]
Reinsurance premium				72
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims				77
Change in Deferred Gain on Retroactive Reinsurance				$ 13
The Navigators Group, Inc. [Member] | Adverse Development Cover Navigators Group [Member] | Maximum
Business Acquisition [Line Items]
Reinsurance Retention Policy, Excess Retention, Amount Reinsured							300
The Navigators Group, Inc. [Member] | Adverse Development Cover Navigators Group [Member] | Retention Layer Above Reserve for the Covered Liabilities as of the Inception Date [Member]
Business Acquisition [Line Items]
Reinsurance Retention Policy, Amount Retained							100
The Navigators Group, Inc. [Member] | Adverse Development Cover Navigators Group [Member] | Retention Layer for Reserve for the Covered Liabilities as of the Inception Date [Member]
Business Acquisition [Line Items]
Reinsurance Retention Policy, Amount Retained							$ 1,816
The Navigators Group, Inc. [Member] | Recorded by Acquiree Prior to Acquisition [Member]
Business Acquisition [Line Items]
Current accident year	52
The Navigators Group, Inc. [Member] | Cash
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 2,098