Employee Benefit Arrangements - Net Periodic Benefit Costs and Other Changes in Plan Assets and Future Amortizaion of Prior Service Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Periodic (Benefit) Costs Recognized in Consolidated Statements of Operations:
Net (gain) loss recognition	$ 15	$ 55	$ (63)
Other Changes in Plan Assets and Benefit Obligations Recognized in AOCI:
Amortization of prior service (credit) cost	15	10	14
Total recognized in AOCI	15	10	14
Pension Plan
Net Periodic (Benefit) Costs Recognized in Consolidated Statements of Operations:
Service cost	24	25	26
Interest cost	93	96	104
Expected return on plan assets	(115)	(104)	(122)
Amortization of prior service cost (credit)	(10)	(10)	(10)
(Gain) loss recognized due to curtailment	1	0	0
Net (gain) loss recognition	14	57	(62)
Net periodic (benefit) costs	7	64	(64)
Other Changes in Plan Assets and Benefit Obligations Recognized in AOCI:
Amortization of prior service (credit) cost	10	10	10
(Credit) cost recognized due to curtailment	2	0	0
Total recognized in AOCI	12	10	10
Total recognized in net periodic (benefit) costs and AOCI	19	74	(54)
Future amortization of prior service cost (credit)	(9)
Other Postretirement Benefits
Net Periodic (Benefit) Costs Recognized in Consolidated Statements of Operations:
Service cost	0	0	0
Interest cost	1	1	1
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	(4)	(3)	(4)
(Gain) loss recognized due to curtailment	0	0	0
Net (gain) loss recognition	1	(2)	(1)
Net periodic (benefit) costs	(2)	(4)	(4)
Other Changes in Plan Assets and Benefit Obligations Recognized in AOCI:
Amortization of prior service (credit) cost	4	0	4
(Credit) cost recognized due to curtailment	0	0	0
Total recognized in AOCI	4	0	4
Total recognized in net periodic (benefit) costs and AOCI	2	$ (4)	$ 0
Future amortization of prior service cost (credit)	$ (4)