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, 2014	Dec. 31, 2013
New York [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	$ 2,262	$ 1,839
Amortized Cost	2,135	1,809
Texas [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,946	1,990
Amortized Cost	1,829	1,904
California [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,507	1,139
Amortized Cost	1,422	1,093
Illinois [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,086	1,116
Amortized Cost	1,022	1,094
Florida [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,080	903
Amortized Cost	1,017	877
Special Revenue Bonds [Member] | New York [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	2,046	1,611
Special Revenue Bonds [Member] | Texas [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	883	930
Special Revenue Bonds [Member] | California [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,098	859
Special Revenue Bonds [Member] | Illinois [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	608	577
Special Revenue Bonds [Member] | Florida [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	850	757
Municipal and Political Subdivision General Obligation Bonds [Member] | New York [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	173	197
Municipal and Political Subdivision General Obligation Bonds [Member] | Texas [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	852	830
Municipal and Political Subdivision General Obligation Bonds [Member] | California [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	153	82
Municipal and Political Subdivision General Obligation Bonds [Member] | Illinois [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	381	483
Municipal and Political Subdivision General Obligation Bonds [Member] | Florida [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	63	38
State General Obligation Bonds [Member] | New York [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	43	31
State General Obligation Bonds [Member] | Texas [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	211	230
State General Obligation Bonds [Member] | California [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	256	198
State General Obligation Bonds [Member] | Illinois [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	97	56
State General Obligation Bonds [Member] | Florida [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	$ 167	$ 108