Business Segments - Adjustments for Difference in Interim Medicare Part D Results for Segment Purposes and GAAP (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Disclosure [Line Items]
Benefit costs deferred	$ 591,897	$ 586,517	[1]
Government risk-sharing premium adjustment	(830,148)	(819,020)	[1]
Pre-tax addition to segment interim period income	18,484	20,276
After tax amount	12,015	13,179
Medicare Part D [Member]
Segment Reporting Disclosure [Line Items]
After tax amount	12,015	13,179
Adjustments [Member]
Segment Reporting Disclosure [Line Items]
Benefit costs deferred	27,229	47,671
Government risk-sharing premium adjustment	(8,745)	(27,395)
Adjustments [Member] | Medicare Part D [Member]
Segment Reporting Disclosure [Line Items]
Government risk-sharing premium adjustment	(8,745)	(27,395)
Pre-tax addition to segment interim period income	$ 18,484	$ 20,276

[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