Employee Benefits - Fair Values of Pension Plan Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 2,946	$ 2,717
Short Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	48	37
Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	993	916
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,850	1,718
Mortgage-backed Securities [Member] | Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	228	217
U.S. Government and Government Agency and Authority Obligations [Member] | Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	209	224
Corporate Bonds [Member] | Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	419	371
Foreign Government and Government Agency Obligations [Member] | Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	137	104
Other Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 55	$ 46