Derivative Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Interest Rate Swaps [Member]

Derivative [Line Items]

Schedule of derivative instruments

Fair Value Hedge of Long-Term Corporate Debt	Notional Value (in millions)
Type of instrument. Interest rate swap contracts	2017		2016
	$	750	$	750
Purpose. To convert a portion of the interest rate exposure on the Company's long-term debt from fixed to variable rates. This more closely aligns the Company's interest expense with the interest income received on its cash equivalent and short-term investment balances. The variable rates are benchmarked to LIBOR.
Terms of derivative instruments. The Company provides upfront margin and settles fair value changes and net interest between variable and fixed rates daily with a central clearinghouse.
Accounting. Using fair value hedge accounting, the fair values of the swap contracts are reported in other assets, including other intangibles, or accounts payable, accrued expenses, and other liabilities. The critical terms of these swaps match those of the long-term debt being hedged. As a result, the carrying value of the hedged debt is adjusted to reflect changes in its fair value driven by LIBOR. The effects of those adjustments on other operating expenses are offset by the effects of corresponding changes in the swaps' fair value. The net impact from the hedge reported in other operating expenses reflects interest expense on the hedged debt at the variable interest rate.

Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Foreign Currency Swaps [Member]

Derivative [Line Items]

Schedule of derivative instruments

Fair Value Hedges of Fixed Maturity Bonds	Notional Value (in millions)
Type of instrument. Foreign currency swap contracts	2017		2016
	$	318	$	78
Purpose. To hedge the foreign exchange related changes in fair values of the Company's fixed maturity bonds.
Terms of derivative instruments. The Company periodically exchanges cash flows between two currencies for both principal and interest. Foreign currency swaps are Euros and British pounds and have terms for up to twelve years.
Accounting. Using fair value hedge accounting, fair values are reported in other long-term investments or accounts payable, accrued expenses, and other liabilities. Changes in fair values of the swap contracts, as well as changes in the fair values of the hedged bonds attributable to the hedged risk, are reported in other realized investment gains and losses.

Non designated [Member] | Forward Contracts [Member]

Derivative [Line Items]

Schedule of derivative instruments

Economic Hedges of a Fixed Maturity Bond Portfolio	Notional Value (in millions)
Type of instrument. Foreign currency forward contracts	2017		2016
	$	255	$	149
Purpose. To hedge the foreign exchange related changes in fair values of a U.S. dollar-denominated fixed maturity bond portfolio to reflect the local currency for one of the Company's foreign subsidiaries.
Terms of derivative instruments. The Company agrees to purchase South Korean won in exchange for U.S. dollars at a future date, generally within three months from the contracts' trade dates.
Accounting. As these arrangements were not designated as accounting hedges, fair values are reported in short-term investments or accounts payable, accrued expenses, and other liabilities, and changes in fair values are reported in other realized investment gains and losses.