Derivative Instruments - Derivatives - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 12,025,000,000		$ 12,025,000,000		$ 13,706,000,000
Cash	173,000,000		173,000,000		185,000,000
Pledged collateral, securities	88,000,000		88,000,000		78,000,000
Cash collateral held	23,000,000		23,000,000		16,000,000
Securities Received as Collateral		$ 1,000,000		$ 1,000,000	1,000,000
Collateral Securities Repledged, Delivered, or Used	0		0		0
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	0		0		0
Asset Pledged as Collateral [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cash	0		0		1,000,000
Over the Counter [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pledged collateral, securities	80,000,000		80,000,000		88,000,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Loss on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring	0	$ 0	0	$ 0
AOCI Attributable to Parent [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			35,000,000
Not Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	9,416,000,000		9,416,000,000		11,396,000,000
Not Designated as Hedging Instrument | Interest rate swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 7,600,000,000		$ 7,600,000,000		$ 7,600,000,000