Fair Value Measurements - Change in Fair Values of Level 3 Financial Instruments (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Securities Available for Sale [Member] \| Other Securities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	$ 20	$ 20
Gains (Losses) Included in Other Comprehensive Income	5	0
Gains (Losses) Included in Earnings	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance	25	20
Unrealized Gains (Losses) Included in Earnings	0	0
Other Investments [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	7	3
Gains (Losses) Included in Other Comprehensive Income	0	0
Gains (Losses) Included in Earnings	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers Other	0	0
Transfers into Level 3	1	4
Transfers out of Level 3	0	0
End of Period Balance		7
Unrealized Gains (Losses) Included in Earnings	0	0
Other Investments [Member] \| Principal Investments Direct [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	1	13
Gains (Losses) Included in Other Comprehensive Income	0	0
Gains (Losses) Included in Earnings	0	(1)
Purchases	1	0
Sales	(1)	0
Settlements	0	0
Transfers Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance		12
Unrealized Gains (Losses) Included in Earnings	0	(1)
Interest Rate [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	5	9
Gains (Losses) Included in Other Comprehensive Income	0	0
Gains (Losses) Included in Earnings	1	(1)
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers Other	0	0
Transfers into Level 3	1	1
Transfers out of Level 3	(4)	(5)
End of Period Balance		4
Unrealized Gains (Losses) Included in Earnings	0	0
Credit [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	0	1
Gains (Losses) Included in Other Comprehensive Income	0	0
Gains (Losses) Included in Earnings	0	(5)
Purchases	(1)	0
Sales	0	0
Settlements	0	4
Transfers Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance	(1)	0
Unrealized Gains (Losses) Included in Earnings	0	0
Other [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	3	3
Gains (Losses) Included in Other Comprehensive Income	0	0
Gains (Losses) Included in Earnings	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers Other	1	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance		3
Unrealized Gains (Losses) Included in Earnings	0	0
Loans Held For Sale Fair Value [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	0	1
Gains (Losses) Included in Other Comprehensive Income	0	0
Gains (Losses) Included in Earnings	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers Other	1	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance	1	1
Unrealized Gains (Losses) Included in Earnings	0	0
Loans Held For Investment Fair Value [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	3	2
Gains (Losses) Included in Other Comprehensive Income	0	0
Gains (Losses) Included in Earnings	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance		2
Unrealized Gains (Losses) Included in Earnings	$ 0	$ 0

Fair value measurement with unobservable inputs reconciliation recurring basis asset and liabilities value.

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- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Other Transfers

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-Publisher FASB
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-Section 50
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- Definition

Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-Publisher FASB
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- Definition

Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-Section 50
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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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