Fair Value of Assets and Liabilities - Change in unrealized gains and losses included in net income for level 3 assets and liabilities (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:
Recurring Level 3 assets	$ 13	$ 3	$ 15	$ 13
Gains (losses) for Level 3 liabilities still held at the balance sheet date, included in earnings	1	0	24	3
Derivatives embedded in life and annuity contracts
Gains (losses) included in net income for Level 3 assets and liabilities:
Gains (losses) for Level 3 liabilities still held at the balance sheet date, included in earnings	1	0	24	3
Municipal
Gains (losses) included in net income for Level 3 assets and liabilities:
Recurring Level 3 assets	0	(3)	0	(3)
Equity securities
Gains (losses) included in net income for Level 3 assets and liabilities:
Recurring Level 3 assets	13	4	15	14
Free-standing derivatives, net
Gains (losses) included in net income for Level 3 assets and liabilities:
Recurring Level 3 assets	0	2	0	3
Other assets
Gains (losses) included in net income for Level 3 assets and liabilities:
Recurring Level 3 assets	$ 0	$ 0	$ 0	$ (1)