Investments (details) - Changes in Net Unrealized Investment Gains - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	$ (1,429)	$ 195	$ (2,196)
Income tax expense (benefit)	(392)	125	(770)
Change in net unrealized gain on investment securities, net of tax	(1,037)	70	(1,426)
Balance, beginning of year	880
Balance, end of year	(157)	880
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	(1,429)	195	(2,196)
Income tax expense (benefit)	(392)	125	(770)
Change in net unrealized gain on investment securities, net of tax	(1,037)	70	(1,426)
Changes in Net Unrealized Gains on Investment Securities [Member]
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	(1,034)	978	(2,731)
Income tax expense (benefit)	(357)	334	(950)
Change in net unrealized gain on investment securities, net of tax	(677)	644	(1,781)
Balance, beginning of year	1,966	1,322	3,103
Balance, end of year	1,289	1,966	1,322
Changes in Net Unrealized Gains on Investment Securities [Member] | Fixed maturities [Member]
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	(893)	913	(2,804)
Changes in Net Unrealized Gains on Investment Securities [Member] | Equity securities [Member]
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	(143)	63	74
Changes in Net Unrealized Gains on Investment Securities [Member] | Other investments [Member]
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	$ 2	$ 2	$ (1)