Fair Value of Assets and Liabilities - Change In Unrealized Gains and Losses included in Net Income for Level 3 (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	$ 6	$ 4	$ 7	$ 9
Total recurring Level 3 liabilities	2	0	25	3
Contractholder funds: Derivatives embedded in life and annuity contracts
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 liabilities	2	0	25	3
Equity securities
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	6	2	7	7
Free-standing derivatives, net
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	0	2	0	3
Other assets
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	$ 0	$ 0	$ 0	$ (1)