Income Taxes - Reconciliation of income taxes at the statutory rate to the provision for income taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Earnings before income taxes (“EBT”)	$ 244	$ 29	$ 678	$ 457
Income taxes at statutory rate	51	10	142	160
Effect of adjustment to prior year taxes	(9)	(2)	(9)	(2)
Effect of tax exempt interest	(3)	(5)	(10)	(17)
Effect of dividends received deduction	(1)	(2)	(3)	(6)
Effect of employee stock ownership plan dividends paid deduction	(1)	0	(2)	(2)
Effect of stock-based compensation	0	(1)	(7)	(14)
Effect of foreign operations	0	1	3	7
Effect of nondeductible expenses	1	2	5	5
Effect of change in valuation allowance	1	16	3	16
Effect of other income tax reconciliation	2	(1)	4	(1)
Provision for income taxes as shown on the Statement of Earnings	$ 41	$ 18	$ 126	$ 146
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income taxes at statutory rate as a percentage of EBT	21.00%	35.00%	21.00%	35.00%
Effect of adjustment to prior year taxes as a percentage of EBT	(4.00%)	(7.00%)	(1.00%)	(1.00%)
Effect of tax exempt interest as a percentage of EBT	(1.00%)	(17.00%)	(1.00%)	(4.00%)
Effect of dividends received deduction as a percentage of EBT	(0.00%)	(7.00%)	(0.00%)	(1.00%)
Effect of employee stock ownership plan dividends paid deduction as a percentage of EBT	(0.00%)	(0.00%)	(0.00%)	(0.00%)
Effect of stock-based compensation as a percentage of EBT	0.00%	(3.00%)	(1.00%)	(3.00%)
Effect of foreign operations as a percentage of EBT	0.00%	3.00%	0.00%	2.00%
Effect of nondeductible expenses as a percentage of EBT	0.00%	7.00%	1.00%	1.00%
Effect of change in valuation allowance as a percentage of EBT	0.00%	55.00%	0.00%	4.00%
Effect of other income tax reconciliation as a percentage of EBT	1.00%	(4.00%)	0.00%	(1.00%)
Provision for income taxes as shown on the Statement of Earnings as a percentage of EBT	17.00%	62.00%	19.00%	32.00%