Business Segments - Adjustments for Difference in Interim Medicare Part D Results for Segment Purposes and GAAP (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	[1]	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Disclosure [Line Items]
Benefit costs deferred	$ 592,293	$ 555,207		$ 1,184,190	$ 1,141,724	[1]
Government risk-sharing premium adjustment	$ (835,567)	$ (799,866)		(1,665,715)	(1,618,886)	[1]
Pre-tax addition to segment interim period income				30,865	25,768
After tax amount				20,062	16,749
Medicare Part D [Member]
Segment Reporting Disclosure [Line Items]
After tax amount				20,062	16,749
Adjustments [Member]
Segment Reporting Disclosure [Line Items]
Benefit costs deferred					63,956
Government risk-sharing premium adjustment				(16,470)	(35,131)
Adjustments [Member] | Medicare Part D [Member]
Segment Reporting Disclosure [Line Items]
Benefit costs deferred				47,335	60,899
Government risk-sharing premium adjustment				(16,470)	(35,131)
Pre-tax addition to segment interim period income				$ 30,865	$ 25,768

[1] Certain balances were retrospectively adjusted to give effect to the adoption of new accounting guidance as described in Note G- Adoption of New Accounting Standards