Fair Value (Fair Value Measurements- Recurring Quantitative Information) (Details) - Fair Value, Measurements, Recurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 6,500	$ 6,400
Recurring Liabilities - Fair Value	(500)	(500)
Total Recurring Assets Net of Recurring Liabilities - Fair Value	6,058	5,944
Loans Held For Sale [Member] | Commercial Mortgages [Member] | Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 92	$ 107
Loans Held For Sale [Member] | Commercial Mortgages [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	5.25%	5.25%
Loans Held For Sale [Member] | Commercial Mortgages [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	15.80%	14.70%
Loans Held For Sale [Member] | Commercial Mortgages [Member] | Discounted Cash Flow [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	10.69%	10.20%
Available-for-sale Securities [Member] | Asset backed [Member] | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 321	$ 332
Available-for-sale Securities [Member] | Asset backed [Member] | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	1.00%	1.00%
Constant default rate (CDR)	2.00%	2.00%
Loss Severity	16.00%	15.00%
Available-for-sale Securities [Member] | Asset backed [Member] | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	19.00%	19.00%
Constant default rate (CDR)	11.80%	11.80%
Loss Severity	100.00%	100.00%
Available-for-sale Securities [Member] | Asset backed [Member] | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	7.90%	7.90%
Constant default rate (CDR)	5.10%	5.40%
Loss Severity	67.10%	68.50%
Spread over the benchmark curve	1.26%	1.79%
Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member] | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 2,545	$ 2,661
Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member] | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	1.00%	1.00%
Constant default rate (CDR)	0.00%	0.10%
Loss Severity	20.00%	15.00%
Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member] | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	33.00%	31.60%
Constant default rate (CDR)	17.80%	18.80%
Loss Severity	100.00%	100.00%
Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member] | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	10.90%	10.80%
Constant default rate (CDR)	5.70%	5.40%
Loss Severity	50.50%	51.50%
Spread over the benchmark curve	1.96%	1.90%
Loans - Residential real estate [Member] | Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 99	$ 104
Loans - Residential real estate [Member] | Discounted Cash Flow [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loss Severity	8.00%	8.00%
Discount rate	5.40%	4.90%
Loans - Residential real estate [Member] | Consensus Pricing [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 142	$ 133
Loans - Residential real estate [Member] | Consensus Pricing [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative default rate	11.00%	11.00%
Loss Severity	0.00%	0.00%
Discount rate	5.50%	5.50%
Loans - Residential real estate [Member] | Consensus Pricing [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative default rate	100.00%	100.00%
Loss Severity	100.00%	100.00%
Discount rate	8.00%	8.00%
Loans - Residential real estate [Member] | Consensus Pricing [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative default rate	82.50%	85.70%
Loss Severity	18.50%	20.60%
Discount rate	5.70%	5.70%
Loans - Home equity [Member] | Consensus Pricing [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 61	$ 61
Loans - Home equity [Member] | Consensus Pricing [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit and Liquidity discount	0.00%	0.00%
Loans - Home equity [Member] | Consensus Pricing [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit and Liquidity discount	99.00%	99.00%
Loans - Home equity [Member] | Consensus Pricing [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit and Liquidity discount	61.10%	61.10%
Equity Investments [Member] | Multiple Of Adjusted Earnings [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 1,129	$ 1,036
Equity Investments [Member] | Multiple Of Adjusted Earnings [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Multiple of earnings	4.9	4.5
Equity Investments [Member] | Multiple Of Adjusted Earnings [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Multiple of earnings	29.7	29.7
Equity Investments [Member] | Multiple Of Adjusted Earnings [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Multiple of earnings	8.3	8.3
Mortgage Servicing Rights [Member] | Residential Mortgage [Member] | Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 1,256	$ 1,164
Mortgage Servicing Rights [Member] | Residential Mortgage [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	0.00%	0.00%
Spread over the benchmark curve	3.46%	3.90%
Mortgage Servicing Rights [Member] | Residential Mortgage [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	44.40%	36.70%
Spread over the benchmark curve	18.11%	18.39%
Mortgage Servicing Rights [Member] | Residential Mortgage [Member] | Discounted Cash Flow [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	8.70%	10.00%
Spread over the benchmark curve	8.31%	8.30%
Mortgage Servicing Rights [Member] | Commercial Mortgages [Member] | Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 723	$ 668
Mortgage Servicing Rights [Member] | Commercial Mortgages [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	7.00%	7.70%
Discount rate	6.30%	6.40%
Mortgage Servicing Rights [Member] | Commercial Mortgages [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	13.70%	14.20%
Discount rate	8.30%	7.90%
Mortgage Servicing Rights [Member] | Commercial Mortgages [Member] | Discounted Cash Flow [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate (CPR)	7.90%	8.50%
Discount rate	8.10%	7.80%
Financial Derivatives [Member] | Visa Class B Swap [Member] | Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Liabilities - Fair Value	$ (363)	$ (380)
Estimated growth rate of Visa Class A share price	16.00%	16.00%
Fair Value Inputs Length Of Litigation Resolution Date	6/30/2021	6/30/2021
Financial Derivatives [Member] | Visa Class B Swap [Member] | Discounted Cash Flow [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated conversion factor of Class B shares into Class A shares	163.80%	163.80%
Insignificant Assets, Net of Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 53	$ 58