Fair Value, Assets Recorded at Fair Value on a Nonrecurring Basis Level 3 Valuation Techniques and Significant Unobservable Inputs (Details) - Nonrecurring [Member] - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans held for sale	$ 5,013	$ 2,446
Total assets recorded at fair value	6,467	4,531
Residential [Member] | Not government insured/guaranteed [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans held for sale	1,800	27
Residential [Member] | Government insured/guaranteed [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans held for sale	1,300	1,200
Nonmarketable equity securities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Nonmarketable equity securities	$ 895	$ 931
Measurement Input, Default Rate [Member] | Discounted cash flow [Member] | Minimum [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	0.30%	0.20%
Measurement Input, Default Rate [Member] | Discounted cash flow [Member] | Maximum [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	5.70%	2.30%
Measurement Input, Default Rate [Member] | Discounted cash flow [Member] | Weighted Average [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	1.40%	1.40%
Measurement Input, Discount Rate [Member] | Discounted cash flow [Member] | Minimum [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	1.50%	1.50%
Measurement Input, Discount Rate [Member] | Discounted cash flow [Member] | Minimum [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	0.00%	10.50%
Measurement Input, Discount Rate [Member] | Discounted cash flow [Member] | Maximum [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	9.50%	8.50%
Measurement Input, Discount Rate [Member] | Discounted cash flow [Member] | Maximum [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	0.00%	10.50%
Measurement Input, Discount Rate [Member] | Discounted cash flow [Member] | Weighted Average [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	4.80%	4.00%
Measurement Input, Discount Rate [Member] | Discounted cash flow [Member] | Weighted Average [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	0.00%	10.50%
Measurement Input, Loss Severity [Member] | Discounted cash flow [Member] | Minimum [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	0.50%	0.50%
Measurement Input, Loss Severity [Member] | Discounted cash flow [Member] | Maximum [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	62.30%	66.00%
Measurement Input, Loss Severity [Member] | Discounted cash flow [Member] | Weighted Average [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	24.70%	1.70%
Measurement Input, Prepayment Rate [Member] | Discounted cash flow [Member] | Minimum [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	5.10%	3.50%
Measurement Input, Prepayment Rate [Member] | Discounted cash flow [Member] | Maximum [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	100.00%	100.00%
Measurement Input, Prepayment Rate [Member] | Discounted cash flow [Member] | Weighted Average [Member] | Residential [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mortgage loans held for sale (residential), measurement input	21.60%	46.50%
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans held for sale	$ 3,148	$ 1,233
Insignificant level 3 assets	84	157
Total assets recorded at fair value	3,232	1,397
Fair Value, Inputs, Level 3 [Member] | Nonmarketable equity securities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Nonmarketable equity securities	83	157
Fair Value, Inputs, Level 3 [Member] | Discounted cash flow [Member] | Residential [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans held for sale	3,148	1,233
Fair Value, Inputs, Level 3 [Member] | Discounted cash flow [Member] | Nonmarketable equity securities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Nonmarketable equity securities	$ 0	$ 7