Derivative Instruments - Derivatives - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount		$ 12,629,000,000	$ 12,730,000,000
Deferred net gains on derivative instruments recorded in AOCI that are expected to be reclassified to earnings during the next twelve months		26,000,000
Collateral receivable		1,000,000	1,000,000
Pledged collateral, securities		72,000,000	101,000,000
Margin Deposit Assets		84	96
Cash collateral held		11,000,000	11,000,000
Securities Received as Collateral		4,000,000
AOCI Attributable to Parent [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
Not Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount		10,356,000,000	10,387,000,000
Designated as Hedging Instrument | Cash Flow Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Ineffectiveness recognized in income with net realized capital gains (losses)	$ 0	0
Interest rate swaps | Not Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount		8,100,000,000	7,300,000,000
Interest rate swaps | Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount		$ 2,120,000,000	$ 2,190,000,000