Quantitative Information about Level 3 Fair Value Measurements of Assets (Detail) (USD $) In Millions, unless otherwise specified						3 Months Ended						3 Months Ended			3 Months Ended			3 Months Ended							3 Months Ended
	Mar. 31, 2012 Fair Value, Measurements, Recurring	Dec. 31, 2011 Fair Value, Measurements, Recurring	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3	Dec. 31, 2011 Fair Value, Measurements, Recurring Level 3	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Available-for-sale State And Political Subdivisions Discounted Cash Flows	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Available-for-sale State And Political Subdivisions Discounted Cash Flows Minimum	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Available-for-sale State And Political Subdivisions Discounted Cash Flows Maximum	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Structured Debt Option Pricing Model	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Structured Debt Option Pricing Model Minimum	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Structured Debt Option Pricing Model Maximum	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Distressed Debt Discounted Cash Flows	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Distressed Debt Discounted Cash Flows Minimum	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Distressed Debt Discounted Cash Flows Maximum	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Structured Foreign Exchange Swaptions Option Pricing Model	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Structured Foreign Exchange Swaptions Option Pricing Model Minimum	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Structured Foreign Exchange Swaptions Option Pricing Model Maximum	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Equity Options Option Pricing Model	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Equity Options Option Pricing Model Minimum	Mar. 31, 2012 Fair Value, Measurements, Recurring Level 3 Trading Assets Equity Options Option Pricing Model Maximum	Mar. 31, 2012 Fair Value, Measurements, Nonrecurring	Dec. 31, 2011 Fair Value, Measurements, Nonrecurring	Mar. 31, 2012 Fair Value, Measurements, Nonrecurring Level 3	Dec. 31, 2011 Fair Value, Measurements, Nonrecurring Level 3	Mar. 31, 2012 Fair Value, Measurements, Nonrecurring Level 3 Loans Discounted Cash Flows	Mar. 31, 2012 Fair Value, Measurements, Nonrecurring Level 3 Loans Discounted Cash Flows Minimum	Mar. 31, 2012 Fair Value, Measurements, Nonrecurring Level 3 Loans Discounted Cash Flows Maximum
Fair Value Inputs Assets Quantitative Information [Line Items]
Expected maturity												3 years	10 years
Fair value of assets	$ 102,442	$ 99,533	$ 324	$ 365	$ 43			$ 29			$ 29			$ 35			$ 37			$ 368	$ 347	$ 44	$ 43	$ 44
Credit spreads												2.00%	9.00%
Expected credit loss						9.00%	41.00%
Correlation risk								15.00%							0.00%	25.00%
Volatility									13.00%	18.00%					13.00%	18.00%		23.00%	32.00%
Timing of sale																									0 months	21 months
Cap rate																									5.50%	8.00%
Cost to complete/sell																									0.00%	29.00%