Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018
Accounting Policy
Tax Cuts and Jobs Act, reclassification from AOCI to retained earnings, tax effect		$ 0
Retained Earnings
Accounting Policy
Tax Cuts and Jobs Act, reclassification from AOCI to retained earnings, tax effect	$ 93	93
AOCI Attributable to Parent
Accounting Policy
Tax Cuts and Jobs Act, reclassification from AOCI to retained earnings, tax effect		$ (93)
Restatement Adjustment | Retained Earnings
Accounting Policy
Tax Cuts and Jobs Act, reclassification from AOCI to retained earnings, tax effect	93
Restatement Adjustment | AOCI Attributable to Parent
Accounting Policy
Tax Cuts and Jobs Act, reclassification from AOCI to retained earnings, tax effect	$ (93)
Minimum
Accounting Policy
Useful life		3 years
Maximum
Accounting Policy
Useful life		40 years