Estimated Effect of Potential Changes in Interest Rates, Credit Spreads and Interest Rate Volatility on Fair Values of Securities Priced by Discounted Cash Flow Pricing Model (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Interest Rates
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	0.50%
Credit Spreads
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	0.50%
Interest Rate Volatility
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	50.00%
Available-for-Sale Fixed Maturity and Perpetual Securities | Interest Rates | Upward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	0.50%
Change in fair value	(1,035)
Available-for-Sale Fixed Maturity and Perpetual Securities | Interest Rates | Downward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	(0.50%)
Change in fair value	1,095
Available-for-Sale Fixed Maturity and Perpetual Securities | Credit Spreads | Upward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	0.50%
Change in fair value	(1,027)
Available-for-Sale Fixed Maturity and Perpetual Securities | Credit Spreads | Downward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	(0.50%)
Change in fair value	1,090
Available-for-Sale Fixed Maturity and Perpetual Securities | Interest Rate Volatility | Upward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	0.50%
Change in fair value	(125)
Available-for-Sale Fixed Maturity and Perpetual Securities | Interest Rate Volatility | Downward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	(0.50%)
Change in fair value	6
Held-to-maturity Securities | Interest Rates | Upward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	0.50%
Change in fair value	(1,596)
Held-to-maturity Securities | Interest Rates | Downward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	(0.50%)
Change in fair value	1,631
Held-to-maturity Securities | Credit Spreads | Upward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	0.50%
Change in fair value	(1,485)
Held-to-maturity Securities | Credit Spreads | Downward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	(0.50%)
Change in fair value	1,489
Held-to-maturity Securities | Interest Rate Volatility | Upward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	0.50%
Change in fair value	(126)
Held-to-maturity Securities | Interest Rate Volatility | Downward Movements
Discounted Cash Flow Pricing Model, by Assumption [Line Items]
Factor Change	(0.50%)
Change in fair value	165