Fair Values of Financial Instruments - Fair Values of Pension Plan Assets Categorized Based Upon Lowest Level of Input (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
Fixed Maturities [Member] | U.S. Government and Government Agency and Authority Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	209	224
Fixed Maturities [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	419	371
Fixed Maturities [Member] | Foreign Government and Government Agency Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	137	104
Fixed Maturities [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	228	217
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,850	1,718
Other Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	55	46
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	657	594
Level 1 [Member] | Short Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 1 [Member] | Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 1 [Member] | Fixed Maturities [Member] | U.S. Government and Government Agency and Authority Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 1 [Member] | Fixed Maturities [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 1 [Member] | Fixed Maturities [Member] | Foreign Government and Government Agency Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 1 [Member] | Fixed Maturities [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	629	573
Level 1 [Member] | Other Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	28	21
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	2,282	2,105
Level 2 [Member] | Short Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	48	37
Level 2 [Member] | Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	993	909
Level 2 [Member] | Fixed Maturities [Member] | U.S. Government and Government Agency and Authority Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	209	224
Level 2 [Member] | Fixed Maturities [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	419	370
Level 2 [Member] | Fixed Maturities [Member] | Foreign Government and Government Agency Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	137	104
Level 2 [Member] | Fixed Maturities [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	228	211
Level 2 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,221	1,145
Level 2 [Member] | Other Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	20	14
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	7	18
Level 3 [Member] | Short Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 3 [Member] | Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		7
Level 3 [Member] | Fixed Maturities [Member] | U.S. Government and Government Agency and Authority Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 3 [Member] | Fixed Maturities [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		1
Level 3 [Member] | Fixed Maturities [Member] | Foreign Government and Government Agency Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 3 [Member] | Fixed Maturities [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		6
Level 3 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Level 3 [Member] | Other Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 7	$ 11