Current weighted average loan to value ratio of commercial mortgage loan.

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Original weighted average loan to value ratio of commercial mortgage loan.

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Percentage of gross unrealized losses depressed less than twenty percent of cost or amortized cost.

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Securities Sold Under Agreements to Repurchase, Percentage of Fair Value Required to be Paid in Cash at Sale

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Variable Interest Entity, Reporting Entity Involvement, Commitments

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The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

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The fair value of available-for-sale securities that serve as collateral for borrowings.

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Amount of transferred financial assets in which the transferor has continuing involvement with the assets underlying the transaction that have been derecognized. Continuing involvement includes, but is not limited to, servicing, recourse, and restrictions on transferor's interests in transferred financial assets.

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This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting.

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Total amount of interest-bearing domestic deposit liabilities, which may include brokered, retail, demand, checking, notice of withdrawal, money market and other interest-bearing deposits.

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Total carrying amount of mortgage loans as of the balance sheet date.

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The carrying amount of the outstanding balance due under the mortgage loan.

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Amount of principal due on loans that have been delinquent, which may exclude loans having interest delinquent for three months or less, as of the balance sheet date.

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The sum of the realized and unrealized net gain (loss) on trading securities during the period.

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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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Amount of transferred financial assets in which the transferor has continuing involvement with the assets underlying the transaction that continue to be recognized in the statement of financial position. Includes, but is not limited to, servicing, recourse, and restrictions on transferor's interests in transferred financial assets.

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Fair value of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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Investments - Additional Information (Details)	3 Months Ended
Investments - Additional Information (Details)	Mar. 31, 2018 USD ($) security	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Concentration Risk [Line Items]
Current Weighted Average Loan to Value Ratio of Commercial Mortgage Loan	51.00%
Original Weighted Average Loan to Value Ratio of Commercial Mortgage loan	61.00%
Net realized capital gains (losses)	$ (30,000,000)	$ 25,000,000
Proceeds from Sale of Available-for-sale Securities	$ 4,300,000,000	4,300,000,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions \| security	2,629
Percentage of AFS securities depressed less than 20% of cost or amortized cost	98.00%
Mortgage loans	$ 3,221,000,000		$ 3,175,000,000
Servicing rights	0		0
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	967,000,000		920,000,000
Fair value of securities on deposit	2,600,000,000		2,500,000,000
Net Realized and Unrealized Gain (Loss) on Trading Securities	(14)
U.S. Treasuries
Concentration Risk [Line Items]
Pledged collateral	$ 46,000,000		104,000,000
Minimum
Concentration Risk [Line Items]
Percentage of fair value received at sale under repurchase agreements	95.00%
Held-for-sale
Concentration Risk [Line Items]
Mortgage loans	$ 0		0
Allowance for Loan and Lease Losses [Member]
Concentration Risk [Line Items]
Mortgage loans	24,000,000		0
Commercial Loan [Member]
Concentration Risk [Line Items]
Mortgage Loans on Real Estate	3,200,000,000
Allowance for Loan and Lease Losses, Real Estate	1,000,000	0	1,000,000	$ 0
Mortgage loans	3,221,000,000		3,175,000,000
Commercial Loan [Member] \| Mortgages [Member]
Concentration Risk [Line Items]
Mortgage loans past due by 90 days or more	0		0
Reclassification out of Accumulated Other Comprehensive Income \| Net Unrealized Gain on Securities
Concentration Risk [Line Items]
Net realized capital gains (losses)	(38,000,000)	$ 14,000,000
Variable Interest Entity, Not Primary Beneficiary [Member]
Concentration Risk [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Commitments	711,000,000		0
Commercial Loan [Member]
Concentration Risk [Line Items]
Loans serviced	1,500,000,000		1,300,000,000
Loans serviced on behalf of third parties	581,000,000		402,000,000
Commercial Loan [Member] \| Investments
Concentration Risk [Line Items]
Loans serviced on behalf of third parties, retained and reported as assets	652,000,000		566,000,000
Commercial Loan [Member] \| Assets Held for Sale
Concentration Risk [Line Items]
Loans serviced on behalf of third parties, retained and reported as assets	$ 225,000,000		$ 356,000,000