Regulatory Matters (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tangible capital (to tangible assets), Actual, Amount	$ 1,408	$ 1,256
Tangible capital (to tangible assets), Actual, Ratio	9.10%	8.88%
Tier 1 capital (to adjusted tangible assets), Actual, Amount	$ 1,408	$ 1,256
Tier 1 capital (to adjusted tangible assets), Actual, Ratio (as a percent)	9.10%	8.88%
Tier 1 capital (to adjusted tangible assets), For Capital Adequacy Purposes, Amount	$ 619	$ 566
Tier 1 capital (to adjusted tangible assets), For Required Adequacy Purposes, Ratio (as a percent)	4.00%	4.00%
Tier 1 capital (to adjusted tangible assets), Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 773	$ 707
Tier 1 capital (to adjusted tangible assets), Well Capitalized Under Prompt Corrective Action Provisions, Ratio (as a percent)	5.00%	5.00%
Common equity Tier 1 capital (to RWA), Actual, Amount	$ 1,196	$ 1,084
Common equity Tier 1 capital (to RWA), Actual, Ratio (as a percent)	12.45%	13.06%
Common equity Tier 1 capital (to RWA), Required for Capital Adequacy, Amount	$ 432	$ 374
Common equity Tier 1 capital (to RWA), Required for Capital Adequacy, Ratio (as a percent)	4.50%	4.50%
Common equity Tier 1 capital (to RWA), Required to Be Well Capitalized, Amount	$ 625	$ 540
Common equity Tier 1 capital (to RWA), Required to Be Well Capitalized, Ratio (as a percent)	6.50%	6.50%
Tier 1 capital (to risk-weighted assets), Actual, Amount	$ 1,408	$ 1,256
Tier 1 capital (to risk-weighted assets), Actual, Ratio (as a percent)	14.65%	15.12%
Tier 1 capital (to risk-weighted assets), For Capital Adequacy Purposes, Amount	$ 577	$ 498
Tier 1 capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio (as a percent)	6.00%	6.00%
Tier 1 capital (to risk-weighted assets), Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 769	$ 664
Tier 1 capital (to risk-weighted assets), Well Capitalized Under Prompt Corrective Action Provisions, Ratio (as a percent)	8.00%	8.00%
Total capital (to risk-weighted assets), Actual, Amount	$ 1,530	$ 1,363
Total capital (to risk-weighted assets), Actual, Ratio (as a percent)	15.92%	16.41%
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Amount	$ 769	$ 664
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio (as a percent)	8.00%	8.00%
Total capital (to risk-weighted assets), Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 961	$ 830
Total capital (to risk-weighted assets), Well Capitalized Under Prompt Corrective Action Provisions, Ratio (as a percent)	10.00%	10.00%
Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tangible capital (to tangible assets), Actual, Amount	$ 1,590	$ 1,491
Tangible capital (to tangible assets), Actual, Ratio	10.26%	10.52%
Tier 1 capital (to adjusted tangible assets), Actual, Amount	$ 1,590	$ 1,491
Tier 1 capital (to adjusted tangible assets), Actual, Ratio (as a percent)	10.26%	10.52%
Tier 1 capital (to adjusted tangible assets), For Capital Adequacy Purposes, Amount	$ 620	$ 567
Tier 1 capital (to adjusted tangible assets), For Required Adequacy Purposes, Ratio (as a percent)	4.00%	4.00%
Tier 1 capital (to adjusted tangible assets), Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 775	$ 709
Tier 1 capital (to adjusted tangible assets), Well Capitalized Under Prompt Corrective Action Provisions, Ratio (as a percent)	5.00%	5.00%
Common equity Tier 1 capital (to RWA), Actual, Amount	$ 1,590	$ 1,491
Common equity Tier 1 capital (to RWA), Actual, Ratio (as a percent)	16.49%	17.90%
Common equity Tier 1 capital (to RWA), Required for Capital Adequacy, Amount	$ 434	$ 375
Common equity Tier 1 capital (to RWA), Required for Capital Adequacy, Ratio (as a percent)	4.50%	4.50%
Common equity Tier 1 capital (to RWA), Required to Be Well Capitalized, Amount	$ 627	$ 542
Common equity Tier 1 capital (to RWA), Required to Be Well Capitalized, Ratio (as a percent)	6.50%	6.50%
Tier 1 capital (to risk-weighted assets), Actual, Amount	$ 1,590	$ 1,491
Tier 1 capital (to risk-weighted assets), Actual, Ratio (as a percent)	16.49%	17.90%
Tier 1 capital (to risk-weighted assets), For Capital Adequacy Purposes, Amount	$ 579	$ 500
Tier 1 capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio (as a percent)	6.00%	6.00%
Tier 1 capital (to risk-weighted assets), Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 772	$ 667
Tier 1 capital (to risk-weighted assets), Well Capitalized Under Prompt Corrective Action Provisions, Ratio (as a percent)	8.00%	8.00%
Total capital (to risk-weighted assets), Actual, Amount	$ 1,712	$ 1,598
Total capital (to risk-weighted assets), Actual, Ratio (as a percent)	17.75%	19.18%
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Amount	$ 772	$ 667
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio (as a percent)	8.00%	8.00%
Total capital (to risk-weighted assets), Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 964	$ 833
Total capital (to risk-weighted assets), Well Capitalized Under Prompt Corrective Action Provisions, Ratio (as a percent)	10.00%	10.00%