Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Cash Flows from Operating Activities
Net income	$ 959	$ 1,205	$ 682
Adjustments to reconcile net income to net cash flows provided by operating activities:
Net investment losses	81	99	199
Other, net	420	(192)	(192)
Net cash flows provided by operating activities	2,571	2,285	2,502
Cash Flows from Investing Activities
Change in short-term investments	147	(274)	155
Other, net	0	(5)	(10)
Net cash flows used by investing activities	(1,317)	(1,843)	(1,512)
Cash Flows from Financing Activities
Dividends paid to common stockholders	(1,025)	(787)	(982)
Proceeds from the issuance of debt	490	491	0
Repayment of debt	(550)	(243)	0
Purchase of treasury stock	(20)	(24)	(39)
Other, net	(12)	(14)	(11)
Net cash flows used by financing activities	(1,117)	(577)	(1,032)
Net change in cash	127	(130)	(61)
Cash, beginning of year	345	475	536
Cash, end of year	472	345	475
Parent Company
Cash Flows from Operating Activities
Net income	959	1,205	682
Adjustments to reconcile net income to net cash flows provided by operating activities:
Equity in net income of subsidiaries	(1,044)	(1,288)	(781)
Dividends received from subsidiaries	995	1,055	990
Other, net	9	2	28
Net cash flows provided by operating activities	919	974	919
Cash Flows from Investing Activities
Change in short-term investments	204	(395)	114
Capital contributions to subsidiaries	(6)	(3)	0
Net cash flows used by investing activities	198	(398)	114
Cash Flows from Financing Activities
Dividends paid to common stockholders	(1,025)	(787)	(982)
Proceeds from the issuance of debt	490	491	0
Repayment of debt	(550)	(243)	0
Purchase of treasury stock	(20)	(24)	(39)
Other, net	(12)	(14)	(11)
Net cash flows used by financing activities	(1,117)	(577)	(1,032)
Net change in cash	0	(1)	1
Cash, beginning of year	1	2	1
Cash, end of year	$ 1	$ 1	$ 2

Capital Contributions to Subsidiaries

No definition available.

Name:	cna_CapitalContributionstoSubsidiaries
Namespace Prefix:	cna_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net amount paid (received) by the reporting entity through acquisition (sale/maturities) of short-term investments with an original maturity that is less than 12 months which qualify for treatment as an investing activity based on management's intention and intended by management to be liquidated, if necessary, within the current operating cycle.

+ References

No definition available.