Fair Value Fair Value - Additional Information (Detail)		Sep. 30, 2016 USD ($) Investment	Dec. 31, 2015 USD ($) Investment	Sep. 30, 2015 USD ($) Investment
Fair Value Measurements [Line Items]
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount | $		$ 0	$ 0	$ 0
Quoted prices percentage of fair value assets	[1],[2]	100.00%	100.00%	100.00%
Internal Pricing | Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Number of securities | Investment		0	0	2
Dealer Quoted Pricing | Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets		1.00%	3.00%	3.00%
Vendor Quoted Pricing | Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets		24.00%	49.00%	47.00%
Vendor Quoted Pricing | Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets		99.00%	97.00%	97.00%

[1] Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2016 and 2015, $185.3 million and $149.9 million, respectively, were included in "other liabilities" and $23.1 million was in "other assets" at December 31, 2015.

[2] The total fair value of the portfolio at September 30, 2016 and 2015, and December 31, 2015 included $1.0 billion, $1.0 billion, and $1.3 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.