Regulatory Requirements (Regulatory Capital and Ratios) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Tier 1 Risk-Based Capital
Actual Amount	$ 7,026
Minimum Capital Requirement Amount	1,396
Minimum to be Well Capitalized Amount	2,094
Actual Ratio	20.10%
Minimum Capital Requirement Ratio	4.00%
Minimum to be Well Capitalized Ratio	6.00%
Total Risk-Based Capital
Actual Amount	7,074
Minimum Capital Requirement Amount	2,792
Minimum to be Well Capitalized Amount	3,490
Actual Ratio	20.30%
Minimum Capital Requirement Ratio	8.00%
Minimum to be Well Capitalized Ratio	10.00%
Tier 1 Leverage
Actual Amount	7,026
Minimum Capital Requirement Amount	4,126
Minimum to be Well Capitalized Amount	5,157
Actual Ratio	6.80%
Minimum Capital Requirement Ratio	4.00%
Minimum to be Well Capitalized Ratio	5.00%
Tangible Equity
Actual Amount	7,026
Minimum Capital Requirement Amount	$ 2,063
Actual Ratio	6.80%
Minimum Capital Requirement Ratio	2.00%