Investments - Net Investment Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	$ 1,535	$ 1,276	$ 1,190
Less: investment expenses	55	50	43
Net investment income	1,480	1,226	1,147
Non-income producing real estate investments and securities partnerships, carrying value	150	191
Fixed maturities [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	1,009	946	899
Equity securities [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	28	14	4
Commercial mortgage loans [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	78	81	91
Policy Loans [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	70	69	72
Other Long Term Investments [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	156	124	98
Short-term investments and cash [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	$ 194	$ 42	$ 26