Investments - Other investments by type (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Other	$ 4,125	$ 3,972
Bank loans
Schedule of Investments [Line Items]
Other	1,702	1,702
Policy loans
Schedule of Investments [Line Items]
Other	894	905
Real estate
Schedule of Investments [Line Items]
Other	769	632
Agent loans
Schedule of Investments [Line Items]
Other	570	538
Other
Schedule of Investments [Line Items]
Other	$ 190	$ 195