Fair Value Measurements (Quantitative Information About Level 3 Measurements) (Details) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Jun. 30, 2015	Dec. 31, 2014
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investment securities available-for-sale	[1]	$ 8,267	$ 8,116
Recurring
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investment securities available-for-sale		8,267	8,116
Recurring | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investment securities available-for-sale		$ 95	$ 136
Recurring | State And Municipal Securities | Minimum | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Unobservable Input, Discount rate	[2]	3.00%	3.00%
Unobservable Input, Workout period	[2]	1 year	1 year
Recurring | State And Municipal Securities | Maximum | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Unobservable Input, Discount rate	[2]	8.00%	9.00%
Unobservable Input, Workout period	[2]	2 years	3 years
Recurring | Equity and Other Non-Debt Securities | Minimum | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Unobservable Input, Discount rate	[2]	4.00%	4.00%
Unobservable Input, Workout period	[2]	1 year	1 year
Recurring | Equity and Other Non-Debt Securities | Maximum | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Unobservable Input, Discount rate	[2]	8.00%	8.00%
Unobservable Input, Workout period	[2]	1 year	2 years

[1] Included auction-rate securities at amortized cost and fair value of $95 million as of June 30, 2015 and $137 million and $136 million, respectively, as of December 31, 2014.

[2] Auction-rate securities.