Income Taxes - Reconciliation of income taxes at the statutory rate to the provision for income taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Earnings before income taxes (“EBT”)	$ 260	$ 205	$ 434	$ 428
Income taxes at statutory rate	54	72	91	150
Effect of stock-based compensation	(2)	(7)	(7)	(13)
Effect of tax exempt interest	(4)	(6)	(7)	(12)
Effect of dividends received deduction	(1)	(2)	(2)	(4)
Effect of employee stock ownership plan dividends paid deduction	(1)	(2)	(1)	(2)
Effect of foreign operations	0	0	3	6
Effect of nondeductible expenses	2	1	4	3
Effect of change in valuation allowance	2	2	2	0
Effect of other income tax reconciliation	2	2	2	0
Provision for income taxes as shown on the Statement of Earnings	$ 52	$ 60	$ 85	$ 128
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 stock-based compensation as a percentage of EBT	(1.00%)	(3.00%)	(2.00%)	(3.00%)
Effect of tax exempt interest as a percentage of EBT	(2.00%)	(3.00%)	(2.00%)	(3.00%)
Effect of dividends received deduction as a percentage of EBT	(0.00%)	(1.00%)	(0.00%)	(1.00%)
Effect of employee stock ownership plan dividends paid deduction as a percentage of EBT	(0.00%)	(1.00%)	(0.00%)	(0.00%)
Effect of foreign operations as a percentage of EBT	0.00%	0.00%	1.00%	1.00%
Effect of nondeductible expenses as a percentage of EBT	1.00%	0.00%	1.00%	1.00%
Effect of change in valuation allowance as a percentage of EBT	1.00%	1.00%	0.00%	0.00%
Effect of other income tax reconciliation as a percentage of EBT	0.00%	1.00%	1.00%	0.00%
Provision for income taxes as shown on the Statement of Earnings as a percentage of EBT	20.00%	29.00%	20.00%	30.00%