Fair Value (Fair Value Measurements- Recurring Quantitative Information) (Details) - Fair Value, Measurements, Recurring [Member] $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 76,591	$ 75,744
Financial and nonfinancial liabilities, fair value disclosure	(3,461)	(3,355)
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, recurring, fair value disclosure	5,800	6,100
Recurring Assets - Fair Value	5,827	6,157
Financial and nonfinancial liabilities, fair value disclosure	(298)	(333)
Total Recurring Assets Net of Recurring Liabilities - Fair Value	5,529	5,824
Level 3 [Member] | Loans Held For Sale [Member] | Commercial Mortgages [Member] | Discounted Cash Flow, Spread Over the Benchmark Curve [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 73	$ 87
Level 3 [Member] | 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	5.30%	5.35%
Level 3 [Member] | 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	20.60%	19.00%
Level 3 [Member] | 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	13.68%	12.17%
Level 3 [Member] | 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	$ 266	$ 274
Level 3 [Member] | 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]
Spread over the benchmark curve	2.20%	1.98%
Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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	$ 2,042	$ 2,128
Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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]
Spread over the benchmark curve	2.06%	2.16%
Level 3 [Member] | 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	$ 90	$ 90
Level 3 [Member] | 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	$ 131	$ 129
Level 3 [Member] | 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%
Level 3 [Member] | 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%
Level 3 [Member] | 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	79.80%	81.80%
Level 3 [Member] | Loans - Home equity [Member] | Consensus Pricing [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 51	$ 53
Level 3 [Member] | 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%
Level 3 [Member] | 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%
Level 3 [Member] | 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	61.20%	61.30%
Level 3 [Member] | 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	$ 1,217	$ 1,255
Level 3 [Member] | 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	5.0	4.5
Level 3 [Member] | 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	19.7	16.0
Level 3 [Member] | 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	8.5	8.4
Level 3 [Member] | 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	$ 1,131	$ 1,257
Level 3 [Member] | 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]
Spread over the benchmark curve	2.80%	4.92%
Level 3 [Member] | 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]
Spread over the benchmark curve	14.38%	14.55%
Level 3 [Member] | 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]
Spread over the benchmark curve	8.05%	8.06%
Level 3 [Member] | 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	$ 681	$ 726
Level 3 [Member] | 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]
Financial and nonfinancial liabilities, fair value disclosure	$ (216)	$ (210)
Estimated growth rate of Visa Class A share price	16.00%	16.00%
Fair Value Inputs Length Of Litigation Resolution Date	12/31/2020	12/31/2020
Level 3 [Member] | 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	163.00%	163.00%
Level 3 [Member] | Insignificant Assets, Net of Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Assets - Fair Value	$ 63	$ 35
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | 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)	0.010	0.010
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | 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)	0.220	0.190
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | 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)	0.082	0.085
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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)	0.010	0.010
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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)	0.362	0.330
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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)	0.105	0.118
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | 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]
Servicing asset, measurement input	0.000	0.000
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | 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]
Servicing asset, measurement input	0.603	0.545
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | 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]
Servicing asset, measurement input	0.105	0.087
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | 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]
Servicing asset, measurement input	0.043	0.046
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | 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]
Servicing asset, measurement input	0.157	0.147
Measurement Input, Constant Prepayment Rate [Member] | Level 3 [Member] | 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]
Servicing asset, measurement input	0.055	0.057
Measurement Input, Constant Default Rate [Member] | Level 3 [Member] | 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)	0.010	0.010
Measurement Input, Constant Default Rate [Member] | Level 3 [Member] | 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)	0.185	0.185
Measurement Input, Constant Default Rate [Member] | Level 3 [Member] | 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)	0.036	0.040
Measurement Input, Constant Default Rate [Member] | Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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)	0.000	0.000
Measurement Input, Constant Default Rate [Member] | Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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)	0.159	0.188
Measurement Input, Constant Default Rate [Member] | Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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)	0.050	0.051
Measurement Input, Loss Severity [Member] | Level 3 [Member] | 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)	0.150	0.150
Measurement Input, Loss Severity [Member] | Level 3 [Member] | 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)	1.000	1.000
Measurement Input, Loss Severity [Member] | Level 3 [Member] | 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)	0.580	0.638
Measurement Input, Loss Severity [Member] | Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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)	0.100	0.100
Measurement Input, Loss Severity [Member] | Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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)	0.957	1.000
Measurement Input, Loss Severity [Member] | Level 3 [Member] | Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [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)	0.493	0.508
Measurement Input, Loss Severity [Member] | Level 3 [Member] | 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]
Loans, Measurement Input	0.080	0.080
Measurement Input, Loss Severity [Member] | Level 3 [Member] | Loans - Residential real estate [Member] | Consensus Pricing [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, Measurement Input	0.000	0.000
Measurement Input, Loss Severity [Member] | Level 3 [Member] | Loans - Residential real estate [Member] | Consensus Pricing [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, Measurement Input	1.000	1.000
Measurement Input, Loss Severity [Member] | Level 3 [Member] | Loans - Residential real estate [Member] | Consensus Pricing [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, Measurement Input	0.165	0.172
Measurement Input, Discount Rate [Member] | Level 3 [Member] | 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]
Loans, Measurement Input	0.055	0.058
Measurement Input, Discount Rate [Member] | Level 3 [Member] | Loans - Residential real estate [Member] | Consensus Pricing [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, Measurement Input	0.055	0.055
Measurement Input, Discount Rate [Member] | Level 3 [Member] | Loans - Residential real estate [Member] | Consensus Pricing [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, Measurement Input	0.083	0.083
Measurement Input, Discount Rate [Member] | Level 3 [Member] | Loans - Residential real estate [Member] | Consensus Pricing [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, Measurement Input	0.058	0.058
Measurement Input, Discount Rate [Member] | Level 3 [Member] | 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]
Servicing asset, measurement input	0.062	0.069
Measurement Input, Discount Rate [Member] | Level 3 [Member] | 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]
Servicing asset, measurement input	0.083	0.085
Measurement Input, Discount Rate [Member] | Level 3 [Member] | 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]
Servicing asset, measurement input	0.082	0.084