Shareholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shareholders Equity [Line Items]
Common stock dividend declared	$ 0.25	$ 0.25	$ 0.25
Common stock dividend paid	$ 0.25	$ 0.25	$ 0.25
Treasury stock repurchased, shares	3.4	33.3	14.6
Purchase of Loews treasury stock	$ 134	$ 1,265	$ 622
CNA Financial [Member]
Shareholders Equity [Line Items]
Purchase of common stock	0.3
Common stock, aggregate cost	$ 8
Subsidiary ownership percentage	90.00%
Increase (decrease) in Additional paid-in capital	$ 3