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
	Mar. 31, 2018	Mar. 31, 2017
Gains (losses) included in net income for Level 3 assets and liabilities:
Recurring Level 3 assets	$ 2	$ 10
Gains (losses) for Level 3 liabilities still held at the balance sheet date, included in earnings	23	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	23	3
Equity securities
Gains (losses) included in net income for Level 3 assets and liabilities:
Recurring Level 3 assets	2	10
Free-standing derivatives, net
Gains (losses) included in net income for Level 3 assets and liabilities:
Recurring Level 3 assets	0	1
Other assets
Gains (losses) included in net income for Level 3 assets and liabilities:
Recurring Level 3 assets	$ 0	$ (1)