Fair Value Measurements (Quantitative Information About Level 3 Measurements) (Details) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Jun. 30, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investment securities available-for-sale	[1]	$ 10,944	$ 10,787
Recurring
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investment securities available-for-sale		10,944	10,787
Recurring | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investment securities available-for-sale		51	54
Recurring | State and municipal securities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investment securities available-for-sale	[2]	$ 5	$ 7
Recurring | State and municipal securities | Minimum | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Unobservable input, discount rate	[2]	5.00%	4.00%
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]	7.00%	6.00%
Unobservable input, workout period	[2]	2 years	2 years
Recurring | Equity and other non-debt securities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investment securities available-for-sale	[2]	$ 46	$ 47
Recurring | Equity and other non-debt securities | Minimum | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Unobservable input, discount rate	[2]	7.00%	7.00%
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]	9.00%	9.00%
Unobservable input, workout period	[2]	2 years	2 years

[1] Included auction-rate securities at amortized cost and fair value of $52 million and $51 million, respectively as of June 30, 2017 and $55 million and $54 million, respectively, as of December 31, 2016.

[2] Auction-rate securities.