Investments - Purchase Credit Impaired (PCI) Investments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Fixed maturity securities
Certain Loans Acquired in Transfer Accounted for as Available-for-sale Debt Securities, Contractually Required Payments Receivable	$ 8,393		$ 9,690
Contractually required payments	6,993		8,026
Less: Cash flows expected to be collected	(7,402)		(8,188)
Cash flows expected to be collected2	7,402		8,188
Less: Amortized cost	(5,698)		(6,168)
Accretable difference	1,704	$ 1,784	2,020
Fair value	6,193		6,703
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Fair Value	1,481		844
Mortgage loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Contractually Required Payments Receivable	2,009		1,140
Contractually required payments	1,666		946
Less: Cash flows expected to be collected	1,971		1,090
Cash flows expected to be collected	1,971		1,090
Accretable difference	515	$ 304	273
Fair value	(1,456)		(817)
Mortgage loans
Fixed maturity securities
Certain Loans Acquired in Transfer, Nonaccretable Difference	38		50
Fixed maturity securities
Fixed maturity securities
Certain Loans Acquired in Transfer, Nonaccretable Difference	$ 991		$ 1,502

Certain Loans Acquired in Transfer Accounted for as Available-for-sale Debt Securities, Amortized Cost

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Certain Loans Acquired in Transfer Accounted for as Available-for-sale Debt Securities, Cash Flows Expected to be Collected

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Certain Loans Acquired in Transfer Accounted for as Available-for-sale Debt Securities, Contractually Required Payments Receivable

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Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Cash Flows Expected to be Collected

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Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Contractually Required Payments Receivable

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Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Fair Value

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The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and other-than-temporary impairments), for certain contractual rights to receive money on demand or on fixed or determinable dates. This relates to loans accounted for as available-for-sale debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans accounted for as available-for-sale debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The aggregate excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan for loans accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The amount of the loan's contractually required payments receivable in excess of the amount of its cash flows expected to be collected. This relates to loans with deteriorating of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Amount of the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

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The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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