Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	760	$ 969
Goodwill	1,057	979	979
Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	5	16
Level 3 [Member] | Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	102	141
Level 3 [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	5	16
Goodwill	1,057	$ 979
Level 3 [Member] | EBITDA Multiple [Member] | Recurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	540.00%	600.00%
Level 3 [Member] | EBITDA Multiple [Member] | Recurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	600.00%	700.00%
Level 3 [Member] | EBITDA Multiple [Member] | Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	550.00%	610.00%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Recurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	550.00%	480.00%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Recurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	620.00%	1040.00%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	580.00%	620.00%
Level 3 [Member] | Revenue Multiple (Where Applicable) [Member] | Recurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	430.00%	110.00%
Level 3 [Member] | Revenue Multiple (Where Applicable) [Member] | Recurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	430.00%	470.00%
Level 3 [Member] | Revenue Multiple (Where Applicable) [Member] | Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	430.00%	400.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	10.00%	10.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	64.00%	100.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	62.00%	36.00%
Level 3 [Member] | Earnings Multiple of Peers [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	1140.00%	1010.00%
Level 3 [Member] | Earnings Multiple of Peers [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	1590.00%	1440.00%
Level 3 [Member] | Earnings Multiple of Peers [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	1292.00%	1159.00%
Level 3 [Member] | Equity Multiple of Peers [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	120.00%	117.00%
Level 3 [Member] | Equity Multiple of Peers [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	122.00%	129.00%
Level 3 [Member] | Equity Multiple of Peers [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	121.00%	124.00%
Level 3 [Member] | Control Premium [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	10.00%
Level 3 [Member] | Control Premium [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	30.00%
Level 3 [Member] | Control Premium [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	19.70%	35.00%
Level 3 [Member] | Weighted-average Cost of Capital [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	13.00%
Level 3 [Member] | Weighted-average Cost of Capital [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	14.00%
Level 3 [Member] | Weighted-average Cost of Capital [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	13.52%	13.00%
Level 3 [Member] | Impaired Loans [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value measurement, valuation technique	Fair value of underlying collateral
Level 3 [Member] | Goodwill [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value measurement, valuation technique	Discounted cash flow and market data
Level 3 [Member] | Other Investments [Member] | Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value measurement, valuation technique	Individual analysis of the condition of each investment