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Estimated Effect of Potential Changes in Interest Rates, Credit Spreads and Interest Rate Volatility on Fair Values of Securities Priced by the Discounted Cash Flow Pricing Model (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2011
Interest Rates | Available-for-Sale Fixed Maturity and Perpetual Securities | Upward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change0.50%
Change in fair value$ (980)
Interest Rates | Available-for-Sale Fixed Maturity and Perpetual Securities | Downward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change(0.50%)
Change in fair value1,048
Credit Spreads | Available-for-Sale Fixed Maturity and Perpetual Securities | Upward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change0.50%
Change in fair value(968)
Credit Spreads | Available-for-Sale Fixed Maturity and Perpetual Securities | Downward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change(0.50%)
Change in fair value1,039
Interest Rate Volatility | Available-for-Sale Fixed Maturity and Perpetual Securities | Upward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change50.00%
Change in fair value(181)
Interest Rate Volatility | Available-for-Sale Fixed Maturity and Perpetual Securities | Downward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change(50.00%)
Change in fair value25
Interest Rates | Held-to-maturity Securities | Upward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change0.50%
Change in fair value(1,682)
Interest Rates | Held-to-maturity Securities | Downward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change(0.50%)
Change in fair value1,751
Credit Spreads | Held-to-maturity Securities | Upward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change0.50%
Change in fair value(1,565)
Credit Spreads | Held-to-maturity Securities | Downward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change(0.50%)
Change in fair value1,583
Interest Rate Volatility | Held-to-maturity Securities | Upward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change50.00%
Change in fair value(250)
Interest Rate Volatility | Held-to-maturity Securities | Downward Movements
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change(50.00%)
Change in fair value$ 238
Interest Rates
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change0.50%
Credit Spreads
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change0.50%
Interest Rate Volatility
 
Derivative Instruments and Hedging Activities Disclosure [Line Items] 
Factor Change50.00%