Fair Value Measurements (Details 4) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Mar. 31, 2012
Discount [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	32.00%
Level 3 [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Other investment		$ 220
Level 3 [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Loans, net of allowance		81
Goodwill		917
Mortgage servicing assets		237
Mortgage servicing assets, Valuation Techniques	Discounted cash flow
Level 3 [Member] | EBITDA multiple [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	6.10%
Level 3 [Member] | EBITDA multiple (where applicable) [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	4.80%
Level 3 [Member] | Revenue multiple (where applicable) [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	0.60%
Level 3 [Member] | Earnings multiple of peers [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Significant unobservable input weighted-average	10.01
Level 3 [Member] | Equity multiple of peers [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Significant unobservable input weighted-average	1.27
Level 3 [Member] | Control premium [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	32.00%
Level 3 [Member] | Weighted-average cost of capital [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	15.00%
Level 3 [Member] | Prepayment speed [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	11.70%
Level 3 [Member] | Expected credit losses [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	2.40%
Level 3 [Member] | Residual cash flows discount rate [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	9.40%
Level 3 [Member] | Value assigned to escrow funds [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	1.80%
Level 3 [Member] | Servicing Cost [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Mortgage servicing assets	2,512
Level 3 [Member] | Loan assumption rate [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	2.18%
Level 3 [Member] | Percentage late [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	0.22%
Other Investments [Member] | Level 3 [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Fair value measurements, valuation techniques	Individual analysis of the condition of each investment
Impaired Loans [Member] | Level 3 [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Fair value measurements, valuation techniques	Fair value of underlying collateral
Goodwill [Member] | Level 3 [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Fair value measurements, valuation techniques	Discounted cash flow and market data
Maximum [Member] | Discount [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	100.00%
Maximum [Member] | Level 3 [Member] | EBITDA multiple [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	8.20%
Maximum [Member] | Level 3 [Member] | EBITDA multiple (where applicable) [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	12.00%
Maximum [Member] | Level 3 [Member] | Revenue multiple (where applicable) [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	4.40%
Maximum [Member] | Level 3 [Member] | Earnings multiple of peers [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Significant unobservable input weighted-average	11.90
Maximum [Member] | Level 3 [Member] | Equity multiple of peers [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Significant unobservable input weighted-average	1.32
Maximum [Member] | Level 3 [Member] | Prepayment speed [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	25.00%
Maximum [Member] | Level 3 [Member] | Expected credit losses [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	3.00%
Maximum [Member] | Level 3 [Member] | Residual cash flows discount rate [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	15.00%
Maximum [Member] | Level 3 [Member] | Value assigned to escrow funds [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	3.75%
Maximum [Member] | Level 3 [Member] | Servicing Cost [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Mortgage servicing assets	17,000
Maximum [Member] | Level 3 [Member] | Loan assumption rate [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	3.00%
Maximum [Member] | Level 3 [Member] | Percentage late [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	2.00%
Minimum [Member] | Discount [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	0.00%
Minimum [Member] | Level 3 [Member] | EBITDA multiple [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	4.80%
Minimum [Member] | Level 3 [Member] | EBITDA multiple (where applicable) [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	5.50%
Minimum [Member] | Level 3 [Member] | Revenue multiple (where applicable) [Member] | Recurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	0.20%
Minimum [Member] | Level 3 [Member] | Earnings multiple of peers [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Significant unobservable input weighted-average	8.30
Minimum [Member] | Level 3 [Member] | Equity multiple of peers [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Significant unobservable input weighted-average	1.21
Minimum [Member] | Level 3 [Member] | Prepayment speed [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	0.00%
Minimum [Member] | Level 3 [Member] | Expected credit losses [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	1.00%
Minimum [Member] | Level 3 [Member] | Residual cash flows discount rate [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	7.00%
Minimum [Member] | Level 3 [Member] | Value assigned to escrow funds [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	0.50%
Minimum [Member] | Level 3 [Member] | Servicing Cost [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Mortgage servicing assets	700
Minimum [Member] | Level 3 [Member] | Loan assumption rate [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Percentage of significant unobservable input weighted-average	0.00%
Minimum [Member] | Level 3 [Member] | Percentage late [Member] | Nonrecurring [Member]
Quantitative Information about Level 3 Fair Value Measurements
Significant unobservable input weighted-average	0.0000