Fair Value (Nonrecurring Fair Value Measurements) (Details) - Fair Value, Nonrecurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	$ 380		$ 380		$ 198
Nonrecurring Assets - Gains (Losses)	(43)	$ (25)	(82)	$ (61)
Nonaccrual Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	346		346		136
Nonrecurring Assets - Gains (Losses)	(38)	(22)	(73)	(55)
OREO and Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	25		25		57
Nonrecurring Assets - Gains (Losses)	(1)	(2)	(2)	(6)
Long-lived Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	9		9		$ 5
Nonrecurring Assets - Gains (Losses)	$ (4)	$ (1)	$ (7)	$ 0

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
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-Publisher FASB
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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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