Fair Value - Level 3 Valuation Inputs (Details) $ in Millions	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	$ 806	$ 837
Derivatives	1,821	171
Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	84,629	88,206
Available-for-sale, at fair value	806	837
Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	47	57
Available-for-sale, at fair value	727	753
Significant Unobservable Inputs (Level 3) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	47	57
Available-for-sale, at fair value	727	753
Derivatives	57	131
Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Derivatives	(25)	(21)
Significant Unobservable Inputs (Level 3) | Recurring | Dealer Mark
Fair Value Inputs, Quantitative Information [Line Items]
Derivatives	82	152
Agency | Significant Unobservable Inputs (Level 3) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	418	431
Agency | Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	47	57
Available-for-sale, at fair value	38	52
Agency | Significant Unobservable Inputs (Level 3) | Recurring | Consensus
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	380	379
Alt-A and subprime private-label securities | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	127	137
Available-for-sale, at fair value	5	5
Alt-A and subprime private-label securities | Significant Unobservable Inputs (Level 3) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	0	0
Available-for-sale, at fair value	0	2
Alt-A and subprime private-label securities | Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value		2
Mortgage revenue bonds | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	141	144
Mortgage revenue bonds | Significant Unobservable Inputs (Level 3) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	141	144
Mortgage revenue bonds | Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	49	50
Mortgage revenue bonds | Significant Unobservable Inputs (Level 3) | Recurring | Single Vendor
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	92	94
Other | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	172	181
Other | Significant Unobservable Inputs (Level 3) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	168	176
Other | Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	1	$ 1
Other | Significant Unobservable Inputs (Level 3) | Recurring | Single Vendor | Total available-for-sale securities | Minimum
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (percent)		0.00093
Other | Significant Unobservable Inputs (Level 3) | Recurring | Single Vendor | Total available-for-sale securities | Maximum
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (percent)		0.00494
Other | Significant Unobservable Inputs (Level 3) | Recurring | Single Vendor | Total available-for-sale securities | Weighted Average
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (percent)		0.00272
Other | Significant Unobservable Inputs (Level 3) | Recurring | Discounted Cash Flow
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, at fair value	$ 167	$ 175
Other | Significant Unobservable Inputs (Level 3) | Recurring | Discounted Cash Flow | Total available-for-sale securities | Minimum | Default Rate
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (percent)	0.02000	0.04090
Other | Significant Unobservable Inputs (Level 3) | Recurring | Discounted Cash Flow | Total available-for-sale securities | Maximum | Default Rate
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (percent)	0.05150	0.04430
Other | Significant Unobservable Inputs (Level 3) | Recurring | Discounted Cash Flow | Total available-for-sale securities | Weighted Average | Default Rate
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (percent)	0.04998	0.04220