Basis of Presentation - Additional Information (Detail) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Subsidiary or Equity Method Investee [Line Items]
Shares excluded from diluted EPS calculation	2.6	2.2	1.4	1.4
CNA Financial Corporation [Member]
Subsidiary or Equity Method Investee [Line Items]
Subsidiary ownership percentage			90.00%
Diamond Offshore Drilling, Inc. [Member]
Subsidiary or Equity Method Investee [Line Items]
Subsidiary ownership percentage			51.00%
Boardwalk Pipeline Partners, LP [Member]
Subsidiary or Equity Method Investee [Line Items]
Subsidiary ownership percentage			53.00%