Variable Interest Entities (Assets and Liabilities of Consolidated VIEs) (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Total liabilities of consolidated VIEs	[1]	$ 930	$ 1,518
Consolidated VIEs for Which the Company is the Investment Manager
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		3,893	4,421
Total liabilities of consolidated VIEs		1,240	1,951
Consolidated VIEs for Which the Company is the Investment Manager | Assets supporting experience-rated contractholder liabilities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		0	0
Consolidated VIEs for Which the Company is the Investment Manager | Equity securities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		39	28
Consolidated VIEs for Which the Company is the Investment Manager | Commercial mortgage and other loans
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		627	617
Consolidated VIEs for Which the Company is the Investment Manager | Other
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		1,409	1,390
Consolidated VIEs for Which the Company is the Investment Manager | Cash and cash equivalents
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		163	164
Consolidated VIEs for Which the Company is the Investment Manager | Accrued investment income
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		5	7
Consolidated VIEs for Which the Company is the Investment Manager | Other assets
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		419	440
Consolidated VIEs for Which the Company is the Investment Manager | Other liabilities
Variable Interest Entity [Line Items]
Total liabilities of consolidated VIEs		310	433
Consolidated VIEs for Which the Company is the Investment Manager | Notes Issued by Consolidated VIEs
Variable Interest Entity [Line Items]
Total liabilities of consolidated VIEs		$ 930	$ 1,518
VIEs Liabilities, maturities obligations (greater than)		5 years	5 years
Consolidated VIEs for Which the Company is the Investment Manager | Available-for-sale | Fixed maturities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		$ 70	$ 69
Consolidated VIEs for Which the Company is the Investment Manager | Trading | Fixed maturities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		1,078	1,623
Consolidated VIEs for Which the Company is the Investment Manager | Held-to-maturity | Fixed maturities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		83	83
Other Consolidated VIEs
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		1,345	1,345
Total liabilities of consolidated VIEs		7	0
Other Consolidated VIEs | Assets supporting experience-rated contractholder liabilities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		9	9
Other Consolidated VIEs | Equity securities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		0	0
Other Consolidated VIEs | Commercial mortgage and other loans
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		0	0
Other Consolidated VIEs | Other
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		90	97
Other Consolidated VIEs | Cash and cash equivalents
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		0	0
Other Consolidated VIEs | Accrued investment income
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		3	4
Other Consolidated VIEs | Other assets
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		171	150
Other Consolidated VIEs | Other liabilities
Variable Interest Entity [Line Items]
Total liabilities of consolidated VIEs		7	0
Other Consolidated VIEs | Notes Issued by Consolidated VIEs
Variable Interest Entity [Line Items]
Total liabilities of consolidated VIEs		0	0
Other Consolidated VIEs | Available-for-sale | Fixed maturities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		269	275
Other Consolidated VIEs | Trading | Fixed maturities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		0	0
Other Consolidated VIEs | Held-to-maturity | Fixed maturities
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		803	810
ASU 2015-02, Wholly-owned by consolidated subsidiaries | Consolidated VIEs for Which the Company is the Investment Manager
Variable Interest Entity [Line Items]
Total assets of consolidated VIEs		$ 1,843	$ 1,716

[1] See Note 4 for details of balances associated with variable interest entities.