Fair Value of Assets and Liabilities - Change in level 3 assets and liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair value assets measured on recurring basis, change in unrealized gain (loss) included in earnings	$ 10	$ (23)	$ (2)
Gains (losses) for Level 3 liabilities still held at the balance sheet date, included in earnings	0	5	19
Gains (losses) for Level 3 assets and liabilities still held at the balance sheet date, included in earnings	10	(18)	17
Realized capital gains and losses
Gains (losses) included in net income for Level 3 assets and liabilities:
Gains (losses) for Level 3 assets still held at the balance sheet date	(8)	(36)	(20)
Net investment income
Gains (losses) included in net income for Level 3 assets and liabilities:
Gains (losses) for Level 3 assets still held at the balance sheet date	19	13	18
Interest credited to contractholder funds
Gains (losses) included in net income for Level 3 assets and liabilities:
Gains (losses) for Level 3 assets still held at the balance sheet date	(10)	(4)	26
Life and annuity contract benefits
Gains (losses) included in net income for Level 3 assets and liabilities:
Gains (losses) for Level 3 assets still held at the balance sheet date	9	9	(7)
Contractholder funds: 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	0	5	19
Municipal
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair value assets measured on recurring basis, change in unrealized gain (loss) included in earnings	(3)	2	(12)
Corporate
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair value assets measured on recurring basis, change in unrealized gain (loss) included in earnings	1	2	11
ABS
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair value assets measured on recurring basis, change in unrealized gain (loss) included in earnings	0	0	2
Fixed income securities
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair value assets measured on recurring basis, change in unrealized gain (loss) included in earnings	(2)	4	1
Equity securities
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair value assets measured on recurring basis, change in unrealized gain (loss) included in earnings	13	(32)	(4)
Free-standing derivatives, net
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair value assets measured on recurring basis, change in unrealized gain (loss) included in earnings	0	5	1
Other assets
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair value assets measured on recurring basis, change in unrealized gain (loss) included in earnings	$ (1)	$ 0	$ 0