Investment Securities (Summary Of Investment Securities) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Held-to-maturity, fair value	$ 803	$ 850
Available-for-sale Debt Securities, Amortized Cost Basis	15,602	13,337
Available-For-Sale Debt Securities, Gross Unrealized Gains, Recognized In O C I	27	18
Available-For-Sale Debt Securities, Gross Unrealized Losses, Recognized In O C I	157	167
Available-for-sale debt securities, Estimated fair value	15,472	13,188
Available-for-sale Securities, Gross Unrealized Gain	27	18
Available-for-sale, Amortized cost	15,736	13,521
Available-for-sale, Gross unrealized losses, Recognized in OCI	157	167
Available-for-sale securities, Estimated fair value	15,606	13,372
amortized cost of investment securities	16,551	14,389
Gross Unrealized Gains of Investment Securities Recognized in OCI	34	23
Gross Unrealized Losses of Investment Securities Recognized in OCI	176	190
Estimated Fair Value of Investment Securities	16,409	14,222
Mutual Funds And Stock [Member]
Investment [Line Items]
Available-for-sale Securities, Gross Unrealized Gain	0	0
Available-for-sale, Amortized cost	134	184
Available-for-sale, Gross unrealized losses, Recognized in OCI	0	0
Available-for-sale securities, Estimated fair value	134	184
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Held-to-maturity, fair value	803	850
Held-to-maturity, Amortized cost	815	868
Available-for-sale Debt Securities, Amortized Cost Basis	1,299	1,182
Available-For-Sale Debt Securities, Gross Unrealized Gains, Recognized In O C I	4	1
Available-For-Sale Debt Securities, Gross Unrealized Losses, Recognized In O C I	18	29
Available-for-sale debt securities, Estimated fair value	1,285	1,154
Held-to-maturity Securities, Unrecognized Holding Gain	7	5
Held-to-maturity Securities, Unrecognized Holding Loss	19	23
Available-for-sale Securities [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	25	25
Available-For-Sale Debt Securities, Gross Unrealized Gains, Recognized In O C I	0	0
Available-For-Sale Debt Securities, Gross Unrealized Losses, Recognized In O C I	1	1
Available-for-sale debt securities, Estimated fair value	24	24
Agency Securities [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,858	1,846
Available-For-Sale Debt Securities, Gross Unrealized Gains, Recognized In O C I	3	2
Available-For-Sale Debt Securities, Gross Unrealized Losses, Recognized In O C I	8	9
Available-for-sale debt securities, Estimated fair value	1,853	1,839
Agency Guaranteed Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	10,060	7,986
Available-For-Sale Debt Securities, Gross Unrealized Gains, Recognized In O C I	12	7
Available-For-Sale Debt Securities, Gross Unrealized Losses, Recognized In O C I	111	110
Available-for-sale debt securities, Estimated fair value	9,961	7,883
Small Business Administration Loan-Backed Securities [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,360	2,298
Available-For-Sale Debt Securities, Gross Unrealized Gains, Recognized In O C I	8	8
Available-For-Sale Debt Securities, Gross Unrealized Losses, Recognized In O C I	19	18
Available-for-sale debt securities, Estimated fair value	$ 2,349	$ 2,288