Investment Securities (Narrative) (Details) $ in Millions		Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Securities with no credit impairment in unrealized loss position		354
Investment securities available-for-sale, Amortized Cost	[1]	$ 11,061	$ 10,829
Investment securities available-for-sale, Fair Value	[1]	10,938	10,787
Investment securities held-to-maturity, Amortized Cost		1,266	1,582
Investment securities held-to-maturity, Fair Value		1,246
Carrying value of securities pledged		800
Liabilities secured by pledged collateral		$ 500
U.S. Treasury and other U.S. government agency securities
Securities with no credit impairment in unrealized loss position		29
Investment securities available-for-sale, Amortized Cost		$ 2,743	2,772
Investment securities available-for-sale, Fair Value		$ 2,727	2,779
Residential mortgage-backed securities
Securities with no credit impairment in unrealized loss position		284
Investment securities available-for-sale, Amortized Cost	[2]	$ 8,230	7,921
Investment securities available-for-sale, Fair Value	[2]	8,124	7,872
Investment securities held-to-maturity, Amortized Cost	[2],[3]	1,266	1,582
Investment securities held-to-maturity, Fair Value	[2],[3]	$ 1,246	$ 1,576
Auction-rate state and municipal securities
Securities with no credit impairment in unrealized loss position		13
Auction-rate preferred securities
Securities with no credit impairment in unrealized loss position		28
Prepayment options | Residential mortgage-backed securities
Investment securities available-for-sale, Fair Value		$ 8,100
Investment securities held-to-maturity, Fair Value		$ 1,200

[1] Included auction-rate securities at amortized cost and fair value of $51 million and $49 million, respectively, as of December 31, 2017 and $55 million and $54 million, respectively, as of December 31, 2016.

[2] Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.

[3] The amortized cost of investment securities held-to-maturity included the unamortized balance of net unrealized losses as of the transfer date of $9 million and $12 million at December 31, 2017 and 2016, respectively, related to securities transferred from available-for-sale, which is included in accumulated other comprehensive loss.