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Derivatives - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Feb. 08, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 13,706,000,000	$ 12,291,000,000
Net reclassifications from AOCI to earnings resulting from the discontinuance of cash-flow hedges due to forecasted transactions that were no longer probable of occurring		0	$ 0
Derivative, Collateral, Right to Reclaim Cash	1,000,000	4,000,000
Pledged collateral, securities	78,000,000	67,000,000
Cash collateral held	16,000,000	9,000,000
Securities collateral held or repledged	1,000,000	5,000,000
Collateral Securities Repledged, Delivered, or Used	0	$ 0
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	0
Information about Sources and Uses of Collateral that is Received Through Resale Agreements and Securities Borrowing Agreements		not sell any securities held as collateral
Over the Counter [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pledged collateral, securities	88,000,000	$ 89,000,000
Reclassification out of Accumulated Other Comprehensive Income
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net reclassifications from AOCI to earnings resulting from the discontinuance of cash-flow hedges due to forecasted transactions that were no longer probable of occurring	0
Accumulated Other Comprehensive Income (Loss), net of tax
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Deferred net gains on derivative instruments recorded in AOCI that are expected to be reclassified to earnings during the next twelve months	16,000,000
Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	2,310,000,000	2,193,000,000
Designated as Hedging Instrument \| Interest rate swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	2,040,000,000	2,040,000,000
Not Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	11,396,000,000	10,098,000,000
Not Designated as Hedging Instrument \| Interest rate swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 7,600,000,000	$ 7,100,000,000
Not Designated as Hedging Instrument \| Contingent capital facility put option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Junior Subordinated Debentures				$ 500,000,000
Maximum [Member] \| Not Designated as Hedging Instrument \| Contingent capital facility put option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount				$ 500,000,000