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Organization, Basis of Presentation and Summary of Significant Accounting Policies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Cash Equivalents [Abstract]
Overnight Cash, Federal Reserve	$ 490	$ 1,100
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI recognized for the period	$ 0	0	$ 0
Loan and Lease Receivables, Impaired [Abstract]
Percentage of Loan To Value, For Assigning Higher Level Of Risk	110.00%
Percentage of Combined Loan To Value, For Assigning Higher Level Of Risk	125.00%
Credit Score For Assigning Higher Level Of Risk	600
Number Of Consecutive Payments For Modified Loans To Be Performing	6
Period For Bankruptcy Loans To Be Classified As Nonperforming	60 days
Loans and Leases Receivable, Other Information [Abstract]
Period Past Due Real Estate Secured Loans Place On Nonaccrual Status And Classified As Nonperforming	90 days
Period Nonperforming Loans Return To Accrual Status	90 days
Number Of Consecutive Payments For Modified Loans To Be Performing	6
Financing Receivable, Allowance for Credit Losses [Line Items]
Trust Preferred Securities Contractual Time Period	30 years
Allowance for loan losses	$ 74	221	353	$ 404
Loans and Leases Receivable, before Fees, Gross	2,717	3,756
Goodwill and Intangible Assets Disclosure [Abstract]
Impairment of goodwill	0	0	0
Equity Method, Cost Method and Other Investments [Abstract]
Investment in FHLB Stock	$ 36	15
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number \| shares	100,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Abstract]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 4 months 24 days
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	58	48	28
Share-based compensation	$ 41	$ 30	$ 34
A2015Plan [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant \| shares	8,900,000
Property And Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Property And Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Software Development [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	4 years
Available-for-sale Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI recognized for the period	$ 0
Held-to-maturity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI recognized for the period	$ 0
Employee Stock Option [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	2 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	7 years
Employee Stock Option [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number Of Common Shares Restricted Stock Unit Can Be Converted Into \| shares	1
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number \| shares	2,500,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Abstract]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 37
Restricted Stock Units (RSUs) [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	1 year
Restricted Stock Units (RSUs) [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares each performance share unit can be converted into \| shares	1
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number \| shares	200,000