Fair Value Level 3 Valuation Inputs (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value Inputs, Quantitative Information [Line Items]
Derivatives	$ 2,734	$ 231
Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	52,941	48,123
Available-for-sale securities	2,289	2,404
Assets, Fair Value Disclosure	65,702	58,623
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	44,727	39,501
Available-for-sale securities	0	0
Assets, Fair Value Disclosure	161,035	89,558
Mortgage loans held-for-sale, at lower of cost or fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	44,727	39,501
Available-for-sale securities	0	0
Assets, Fair Value Disclosure	44,727	39,501
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	8,052	8,576
Available-for-sale securities	1,521	1,612
Assets, Fair Value Disclosure	3,439,362	3,313,691
Mortgage loans held-for-sale, at lower of cost or fair value	86	229
Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	8,052	8,576
Available-for-sale securities	1,521	1,612
Assets, Fair Value Disclosure	21,297	18,685
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	4	274
Liabilities, Fair Value Disclosure	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	162	46
Available-for-sale securities	768	792
Assets, Fair Value Disclosure	128,464	136,048
Mortgage loans held-for-sale, at lower of cost or fair value	8,402	7,054
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	162	171
Available-for-sale securities	768	792
Derivatives	217	162
Assets, Fair Value Disclosure	1,815	1,725
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Derivatives	8	15
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Dealer Mark [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Derivatives	209	147
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	6,019	2,598
Mortgage loans held-for-sale, at lower of cost or fair value	3,653	1,076
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Nonrecurring [Member] | Single Vendor Without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	1,886	605
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Nonrecurring [Member] | Consensus Without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	1,767	471
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	188
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	68	46
Available-for-sale securities	75
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus Without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	113	107
Private-label and other mortgage securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	444	629
Available-for-sale securities	7	57
Private-label and other mortgage securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	0	0
Available-for-sale securities	0	0
Private-label and other mortgage securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	350	629
Available-for-sale securities	7	57
Private-label and other mortgage securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	94	0
Available-for-sale securities	0	0
Mortgage revenue bonds [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	296	315
Mortgage revenue bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	0	0
Mortgage revenue bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	0	0
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	296	315
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	211	222
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	94	64
Available-for-sale securities	85	93
Other [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	291	314
Other [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	0	0
Other [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	7	8
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	284	306
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	36	39
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	$ 248	$ 267
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale Securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)	32.50%	23.00%
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale Securities [Member] | Minimum [Member] | Measurement Input, Default Rate [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Debt Securities, Available-for-sale, Measurement Input (%)	620.0	300.0
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale Securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)	376.00%	205.10%
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale Securities [Member] | Maximum [Member] | Measurement Input, Default Rate [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Debt Securities, Available-for-sale, Measurement Input (%)	620.0	300.0
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale Securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)	97.50%	76.10%
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale Securities [Member] | Weighted Average [Member] | Measurement Input, Default Rate [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Debt Securities, Available-for-sale, Measurement Input (%)	620.0	300.0