Invested Assets and Related Income - Fair Value and Amortized Cost of Tax Exempt Fixed Maturities Other Than Pre-Refunded Bonds (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Texas [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	$ 2,361	$ 2,466
Amortized Cost	2,171	2,269
New York [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,603	1,560
Amortized Cost	1,487	1,444
Illinois [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,260	1,177
Amortized Cost	1,161	1,102
California [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,189	1,374
Amortized Cost	1,089	1,278
Florida [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	912	877
Amortized Cost	844	825
Special revenue bonds [Member] | Texas [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,041	1,035
Special revenue bonds [Member] | New York [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,401	1,385
Special revenue bonds [Member] | Illinois [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	683	617
Special revenue bonds [Member] | California [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	888	994
Special revenue bonds [Member] | Florida [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	771	726
Municipal and political subdivision general obligation bonds [Member] | Texas [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,053	1,156
Municipal and political subdivision general obligation bonds [Member] | New York [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	169	139
Municipal and political subdivision general obligation bonds [Member] | Illinois [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	518	486
Municipal and political subdivision general obligation bonds [Member] | California [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	107	140
Municipal and political subdivision general obligation bonds [Member] | Florida [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	27	12
State general obligation bonds [Member] | Texas [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	267	275
State general obligation bonds [Member] | New York [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	33	36
State general obligation bonds [Member] | Illinois [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	59	74
State general obligation bonds [Member] | California [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	194	240
State general obligation bonds [Member] | Florida [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	$ 114	$ 139