Investments - Other investments by type (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Other	$ 4,075	$ 3,972
Bank loans
Schedule of Investments [Line Items]
Other	1,608	1,702
Policy loans
Schedule of Investments [Line Items]
Other	900	905
Real estate
Schedule of Investments [Line Items]
Other	776	632
Agent loans
Schedule of Investments [Line Items]
Other	597	538
Other
Schedule of Investments [Line Items]
Other	$ 194	$ 195