General (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net unrealized gains (losses) on investments		$ (159)	$ 24	$ (757)	$ 164
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax						$ (50)	$ 0
Accumulated Other Comprehensive (Loss) Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax						(16)	$ 0
ASU 2016-01 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax	$ 28
ASU 2016-01 | Accumulated Other Comprehensive (Loss) Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax						(28)
ASU 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net unrealized gains (losses) on investments	142
Decrease in unrecognized pension and postretirement benefits	130
ASU 2018-02 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax	(12)
ASU 2018-02 | Accumulated Other Comprehensive (Loss) Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax	$ 12					$ 12
Loews | CNAF Consolidated
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Noncontrolling interest, ownership percentage by parent		89.00%		89.00%
Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Realized gains (losses) on equity securities		$ (2)		$ (2)
Common Stock | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Realized gains (losses) on equity securities		(1)		1
Change in fair value of equity securities recognized in other comprehensive income			1		1
Preferred stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Realized gains (losses) on equity securities		2		(23)
Preferred stock | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Realized gains (losses) on equity securities		$ 2		$ (23)
Change in fair value of equity securities recognized in other comprehensive income			$ 1		$ 7