Fair Value, Assets Recorded at Fair Value on a Nonrecurring Basis Level 3 Valuation Techniques and Significant Unobservable Inputs (Details) - Nonrecurring [Member] $ in Millions	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans held for sale	$ 4,318	$ 5,837
Total assets recorded at fair value	6,871	8,203
Other assets	599	386
Residential [Member] | Non-government insured/guaranteed [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans held for sale	1,600	2,500
Residential [Member] | Government insured or guaranteed [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans held for sale	1,300	1,300
Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities	$ 1,483	$ 1,481
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, measurement input	0.40%	0.30%
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, measurement input	51.30%	48.30%
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, measurement input	7.20%	4.60%
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, measurement input	1.50%	1.50%
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, measurement input	8.70%	9.40%
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, measurement input	4.10%	4.30%
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, measurement input	0.50%	0.40%
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, measurement input	72.10%	100.00%
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, measurement input	16.20%	23.40%
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, measurement input	5.00%	4.80%
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, 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, measurement input	23.80%	23.20%
Measurement input, multiples [Member] | Market comparable pricing [Member] | Minimum [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	0.1
Measurement input, multiples [Member] | Market comparable pricing [Member] | Maximum [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	11.6
Measurement input, multiples [Member] | Market comparable pricing [Member] | Weighted average [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	4.9
Measurement input, comparability adjustment [Member] | Market comparable pricing [Member] | Minimum [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	(1.000)
Measurement input, comparability adjustment [Member] | Market comparable pricing [Member] | Maximum [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	(0.060)
Measurement input, comparability adjustment [Member] | Market comparable pricing [Member] | Weighted average [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	(0.455)
Measurement input, company risk factor [Member] | Valuation technique, other [Member] | Minimum [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	(1.000)
Measurement input, company risk factor [Member] | Valuation technique, other [Member] | Maximum [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	(0.200)
Measurement input, company risk factor [Member] | Valuation technique, other [Member] | Weighted average [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities, measurement input	(0.409)
Fair value, inputs, level 3 [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage loans held for sale	$ 2,868	$ 3,803
Insignificant level 3 assets	2	201
Total assets recorded at fair value	4,102	4,004
Other assets	390	27
Fair value, inputs, level 3 [Member] | Nonmarketable equity securities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Other assets	390
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities	844	173
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	2,868	$ 3,803
Fair value, inputs, level 3 [Member] | Valuation technique, other [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities	226
Fair value, inputs, level 3 [Member] | Measurement input, multiples [Member] | Market comparable pricing [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities	658
Fair value, inputs, level 3 [Member] | Measurement input, comparability adjustment [Member] | Market comparable pricing [Member] | Nonmarketable equity securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Nonmarketable equity securities	$ 348